Blood, in man and the higher animals, the red liquid which circulates in the cavities of the heart, the arteries, the veins, and the capillary vessels. I. Physical Qualities of the Blood. In the living body the blood is a some-w hat tenacious liquid, containing innumerable solid particles (the blood globules), which are seen only with the microscope. In the arteries the blood is more or less of a light vermilion tint in children, and of a purplish or bright cherry red in adults, and somewhat darker in old people and in pregnant women. In the veins it is dark red, and even blackish. In disease, and also in various physiological states, the blood may be very dark in the arteries, and in other cases very bright in the veins. The peculiar odor of the blood usually resembles that of the perspiration of the individual from whom the blood has been taken. The blood is transparent when seen in thin layers; opaque otherwise. The specific gravity of normal human blood averages 1.055, its physiological limits being 1.045 and 1.075. The minimum of density is in pregnant women and in children, and the maximum in adult men. The capacity of the blood for heat is, according to Nasse, in an exact ratio to its density.

II. Quantity of Blood in the Human Body. Of the various means employed to find out the relative amount of blood in the body, that which consists in first weighing an animal, then taking out as much of its blood as possible, and weighing the latter, is not to be relied on, as the blood never flows out entirely from the blood vessels. However, as it is interesting to know how much blood may escape from divided blood vessels, we will give a list of the results obtained by various experiments. In the ewe the weight of the blood is to the weight of the body as 1 to 22 or 23; in the ox as 1 to 12 (Herbst), or 1 to 23 or 24 (Wanner); in the cow, as 1 to 21.77; in the sheep, as 1 to 20 or 27.72; in the dog, as 1 to 10 or 12, or 21; in the horse, as 1 to 18; in the lamb, as 1 to 20 or 22; in the cat, as 1 to 22; in the rabbit, as 1 to 24 or 29; in the ass, as 1 to 23; in the f«>x, as 1 to 21; in the mouse, as 1 to 22.5. From these results, it has been concluded that in man the proportion of blood is from 1/20 .to 1/10, and therefore, for a man weighing 1(50 lbs., the quantity of blood is from 8 to 16 lbs.

But Haller relates many cases of hemorrhage in which men and women have lost 9, 10, 11, 15, 18, or 22 lbs., or even 30 lbs. of blood from the Dose, and 12 lbs. in one night, or 8 pints, by vomiting (gastrorhagia). Burdach says that Wrisberg has seen a woman who died from a loss of 26 lbs. of blood from the uterus, and that another woman after decapitation yielded 24 lbs. of blood. From facts of this kind Haller, Quesnay, and Hoffmann interred that there is about 28 lbs. of blood in the body of a man of average size. The best mode of estimating the amount of blood in a man has been employed by Lehmann and E. Weber. They determined the weight of two criminals both before and after decapitation. The quantity of the blood which escaped from the body was ascertained in the following manner: water was injected into the vessels of the trunk and head, until the fluid escaping from the veins had only a pale red or yellow color; the quantity of the blood remaining in the body was then calculated, by instituting a comparison between the solid residue of this pale red aqueous fluid, and that of the blood which first escaped. By way of illustration, we subjoin the results yielded by one of the experiments.

The living body of one of the criminals weighed 60,140 grammes, and the same body, after decapitation, 54,600grammes; consequently, 5,540 grammes of blood had escaped; 28.56 grammes of this blood yielded 5.36 grammes of solid residue; 60.5 grammes sanguineous water, collected after the injection, contained 3.724 grammes of solid substances; 6.050 grammes of the sanguineous water that returned from the veins were collected, and these contained 37.24 grammes of solid residue, which corresponds to 1,980 grammes of blood; consequently, the body contained 7,520 grammes of blood (5,540 escaping in the act of decapitation, and 1,980 remaining in the body); hence, the weight of the whole of the blood was to that of the body nearly in the ratio of 1 to 8. The other experiment yielded a precisely similar result. By this mode of calculation, which gives a nearer approximation than any other to the proportion of blood, we have not, however, the exact proportion, because blood remains in some of the capillaries. The only positive conclusion we can draw from these experiments is that there is at least 20 lbs. of blood in the body of a healthy man weighing 160 lbs.

Valentin has employed another mode of calculation, which, unlike the preceding, has given a proportion of blood in the body greater than that which really exists. He bleeds an animal, and determines the proportion of solid parts in the blood; then a certain quantity of water is injected into the veins, and immediately afterward blood is drawn again, and its proportion of solid parts determined; and after a comparison of the two results, a calculation is made which gives the quantity of blood. In dogs it was found that the amount of blood, compared to the weight of the body, is as 1 to 4 1/2, and in sheep as 1 to 5. If this result be applied to man, we find, for a man weighing 160 lbs., from 32 to 36 lbs. of blood, which is most probably an over-estimate. Dr. Blake, by another method, has obtained more important results. He injects into the veins of an animal a certain quantity of the sulphate of alumina, a salt which is not quickly destroyed in the blood, or expelled from it; then he analyzes the blood, and by the proportion of this salt found in it he ascertains very nearly the quan-tity of blood in the body of the animal. The conclusion is that there is 1 lb. of blood for 8 or 9 of the animal, and therefore from 18 to 20 lbs. of blood in a man weighing 160 lbs.

From all these facts it results that the quantity of blood in an adult man is very likely a little above 20 lbs. There is more blood in men than in women. It is not positively determined whether a fat or a lean person has most blood; but Schultz says that there is more blood in lean oxen than in fat ones. Berard justly remarks that it is a mistake to believe that there is proportionally more blood in newly born children than in adults. III. Composition of the Blood. There is no fluid in the body having so complex a composition as the blood. This fact may be easily understood, as we know that through the blood passes everything that is going to or coming from all parts of the body, either solid or liquid. The chemical analysis of the blood is extremely difficult, and much is still to be learned as regards its composition. On comparing the results obtained by various experimenters who have analyzed the blood, we find a great difference between them. Gorup-Besanez has proved that these differences depend mostly on the method of analysis; for he found that when four samples of the same blood were analyzed by himself according to the four principal methods, the results were strikingly different, as the following table will show:

Authors Of The Various Methods



Becquerel and Rodier.








Solid matters...



















Extractive matters and salts.





Hence it is of no value to compare researches on the composition of blood in disease in men at different ages, or in different animals, made by experimenters who have employed different methods. The following table represents the composition of normal human blood, according to the researches of Lehmann. It will be seen that the proportion of corpuscles is notably larger than in the former table.

1. Water..........................................


2. Solid residue 204.55.



2. Corpuscles



Globuline & cell membrane..





6. Mineral substances, exclusive of iron



Sulphuric acid...


Phosphoric acid.






Phosphate of


Phosphate of


This is another proof of the differences due to methods of analysis: in the last case, the corpuscles of the blood have not been deprived of their salts, and therefore their weight is more considerable than in cases where they lose a part of their constituents before being weighed. Many other substances are found in the blood besides those above enumerated. Among the fatty matters we find the saponifiable fats (which chiefly consist of oleate and margarate of soda), a phosphorized fatty matter, choles-terine, and seroline. Besides these substances, there is probably also one or many volatile fatty acids, to which the blood owes its odor. The so-called extractive substances of the blood are very different from each other, some of them being nitrogenized matters, while others are not. Among these substances are found what Mulder calls binoxide and tri-toxide of proteine and sugar, urea, uric and hippuric acids, creatine, creatinine, etc. In the blood vessels, and during life, blood consists essentially of two parts, which differ extremely: one is solid, the corpuscles or globules, the other is liquid, the liquor sanguinis. According to Lehmann, the corpuscles form fully one half of the volume of the blood.

Their analysis compared to that of the liquor sanguinis shows that they differ much from it:

1,000 Parts Of Blood Corpuscles Contain


Solid residue..........312.00

Haematine (including iron)............... 16.75

Globuline and cell membrane .............. 232.22

Fat.................. 2..31

Extractive matters___ 2..60

Mineral substances___ 8..12

1. Chlorine........... 1.686

2. Sulphuric acid...... 0.066

3. Phosphoric acid.... 1.134

4. Potassium......... 3.328

5. Sodium............ 1.052

6. Oxygen............ 0.667

7. Phosphate of lime.. 0.114

8. Phosphate of magnesia............... 0.073

1,000 Parts Of Liquor Sanguinis Contain


Solid residue.......... 97.10

Fibrine............... 4.05

Albumen............. 73.84

Fat................... 1.72

Extractive matters.... 3.94

Mineral substances___ 8.55

1. Chlorine........... 3.644

2. Sulphuric acid..... 0.115

3. Phosphoric acid.... 0.191

4. Potassium......... 0.323

5. Sodium............ 3-341

6. Oxygen............ 0.403

7. Phosphate of lime.. 0.311

8. Phosphate of magnesia............... 0.222

Of the many metals found in the blood, the most important seems to be iron, which is found not only in the blood, but, according to M. Verdeil, in all the coloring matters of the body. Iron in the blood is found only in the corpuscles, combined with the coloring matter, the haematine. According to Lecanu, there is 7 per cent, of iron in haematine. In 15 kilogrammes (33 lbs.) of blood, the proportion of hae-matine is about 34 grammes (1 oz.), and therefore the quantity of iron is nearly 2.42 grammes (nearly 50 grains). Copper was found in the blood by Sarzeau, and manganese by Denis. Millon ascertained the constant existence of these two metals, and also of lead, in the blood. These metals exist in greater quantity in the globules than in the liquor sanguinis. It is very important to know that these metals, and particularly copper, exist normally in the blood, to avoid mistakes that might be made in cases of suspected poisoning by them. It has been said that arsenic exists normally in blood, but this assertion has been disproved. Nickles has pointed out the existence of an interesting element in blood, fluorine.

The blood of man differs from that of woman, as will be seen by the following comparative analyses made by Becquerel and Rodier:



Density of defibrinated blood..........















Extractive matters and free salts......



Fatty matters....






Phosphorized fatty matter.....






Animal soap....



The same chemists have also found that there is less iron in the blood of woman than in that of man. The blood of children is richer in solid constituents, and especially blood corpuscles, than that of adults. It is just the reverse with the blood of old people compared to that of adults. During pregnancy the blood contains more water than in other circumstances; the quantity of albumen and of blood corpuscles is diminished. Cazeaux has justly pointed out that the so.called plethora of pregnant women is not a plethora of blood, but of water, and that it is usually very wrong to bleed women during pregnancy only because they seem to have too much blood. Among animals, the blood of omnivora and carnivora is richer in organic solid constituents than that of the her. bivora. So also is that of the warm.blooded vertebrata, compared to the cold.blooded. The blood of the arteries differs from that of the veins in many points. Its corpuscles have a smaller quantity of solid constituents, especially fats, but they contain relatively more hsema. tine and salts. It has more fibrine and more water, and therefore relatively less albumen. It has also a much smaller quantity of fats, and a much greater amount of extractive matters, while its salts are diminished.

For the composition of the blood of the portal and hepatic veins, see Liver. - Changes in the composition of the blood are effected very quickly; during digestion, for instance, the solid constituents of the blood manifestly increase, while the reverse takes place during lasting. In all the circumstances which modify the blood, it is chiefly the number and the composition of the blood corpuscles which change. The differences between different animals as to the quantity of blood corpuscles are very great; for instance, the pig has 145.5 of dry blood corpuscles, while the goat has only 86.0, out of 1,000 parts of blood. Of course this relates only to dried corpuscles, as Lehmann has found that the normal corpuscles in man form more than one half the quantity of the blood. When it is said that the proportion of corpuscles is only 141/1000 of the blood, this relates to dry corpuscles. The proportion of this most important element in the blood of man is put down at a higher or lower amount, according to the means employed to separate or to dry them.

In this way we may explain how Lehmann gives the proportion of 149.485 for the dry corpuscles in 1,000 parts of blood, while Bec. querel and Kodier give the propoition of 141.1, Richardson 134.8, Lecanu 132.5, Prevost and Dumas 129.0, Andral and Gavarret 127.0, Popp 120.0, Nasse 116.5, and Scherer only 112.0, for the blood of man. The quantity of fibrine in the blood, even in very weak anaemic or hydremic persons, increases in ail cases of inflammation accompanied with fever. IV. Microscopical Study of the Blood. When the blood is examined with a microscope, many things may be found: 1, red corpuscles or disks; 2, white, or rather colorless, corpuscles; 3, molecular elements; 4, pigment; 5, crystals; C, coagulated fibrine. We will study successively these different elements. 1. Red corpuscles or disks. Their discovery is due to Mal. pighi (in 1666), although it seems that Swam. merdam had seen them a few years before. They are found in the blood of all the verte. brata. Their form varies much in animals of different classes. In man they are thick, circular, slightly biconcave disks, consisting of a colorless investing membrane, and of red or, in refracted light, yellow, viscid, fluid contents. They have no nucleus, at least in adult men.

In the other mammalia the red corpuscles are more or less similar to those of man - except, however, a few tribes (camel, dromedary, llama), in which the red corpuscles are not circular and concave, but elliptic and biconvex. In birds they are also elliptic or oval, and elevated in the centre. In amphibia they are oval also, and strongly convex. We owe to the laborious researches of Gulliver the indication of the size of the red corpuscles in an immense number of animals. We will take from the table he has published only what relates to man and to the most common animals, or to those which have corpuscles of the most remarkable size. The measurements are all made in vulgar fractions of an English inch; but for the sake of convenience, the numerator, being invariably 1, is omitted, an 1 the denominators only are printed. These measures show that the size of the blood corpuscles is not at all in proportion with the size of the animal For instance, the corpuscles of man are larger than those of the ass, the horse, the bear, the lion, the tiger, etc, which are larger animals than man. It is nevertheless remarkable that the elephant and the whale are among the animals whose blood corpuscles are the largest.

In the same individual the blood disks are not all of the same size; in man their diameter varies between 1/4800 to 1/2500 of an inch, the average being 1/3200. The red corpuscles of man, although larger than those of most of the mammalia, are so small (the 1/3200 part of an inch) that, according to Home, 19,880 of these corpuscles, placed side by side, would cover only a surface of a square inch. Young says that to cover such a surface 255,000 corpuscles would be necessary. The number of red corpuscles in the body of a man is immense. To convey an idea of this number, we will merely state that, according to Stoltzing, there are from three to four or five millions of corpuscles in one cubic millimetre (the linear millimetre being about fa of an inch). Vierordt and Voelcker had already obtained analogous results. The red corpuscles are very elastic and pliant, so much so that they may pass through blood vessels the diameter of which is somewhat smaller than theirs. They exist in all the vertebrata except one, the lancelet (amphioxus lanceolatus), a very singular and little developed fish. 2. White or colorless corpuscles. These globules seem to have been seen for the first time by the celebrated Hewson, in the last century. However, it is only in our days that they have been well studied.

They are found in all the vertebrata, including the amphibia, whose blood has no other corpuscle. They are much more globular than the red corpuscles, but not perfectly spherical; they have a granular capsule and a nucleus of several small ones. They are quite pale or colorless; they do not contain iron, and have much more fat than the red corpuscles. Their size hardly varies in the different classes of animals, so that they are in some smaller and in others larger than the red corpuscles, which vary much in size. In warm-blooded animals (man included) they average rather more than 1/3000 of an inch diameter. An interesting fact concerning the pale corpuscles of the blood is, that they seem to be endowed with the faculty of altering their form. According to the discovery of Mr. Wharton Jones, and to the more recent researches of M. Davaine, they often show a slow protrusion from their membranous wall; after which another one forms itself in another part, while the first slowly disappears; sometimes a depression is formed instead of a protrusion. These changes have been seen even in circulating blood in living animals. These spontaneous alterations of form have been considered by some physiologists as a proof that these cells or corpuscles are microscopical animals.

But apparently spontaneous movements are not sufficient signs of independent life, for, admitting that these corpuscles are animalcules, Brown-Sequard has shown that all the muscles of man or of animals, separated from the body, may have apparently spontaneous movements; so that we should have to admit that each elementary muscular fibre is a distinct animal being, if apparently spontaneous motions were a proof of the existence of an independent living organism. The number of colorless cells is very much smaller than that of the red disks. There is one colorless corpuscle to 300 or 400 red, according to Donders and Moleschott. The number of colorless cells increases more than that of the red disks after eating, and particularly after taking albuminous food. 3. Molecular elements. There is in the blood a number of exceedingly small solid particles which the French (Donne, Robin) call globulins (small globules). Their nature is unknown, and their form has no definite character; it may be that they are particles of coagulated fibrine. 4. Pigment. There is frequently, and perhaps always, in the blood of man and of the higher animals, a small quantity of black pigment under various forms.

Sometimes there are only exceedingly fine granules, like those of the skin (which are the cause of its color); in other cases there are plates of pigment, which seem chiefly to result from an aggregation of granules. The presence of cells containing black pigment is very rare in the blood. From the researches of Brown-Sequard, it seems that the quantity of pigment increases in the blood of animals when the supra-renal capsules have been extirpated. The accumulation of pigment in the blood of man, according to Planer, and in that of animals, according to Brown-Sequard, is a cause of rapid death. 5. Crystals. It happens, though very rarely, that without any preparation the blood corpuscles become decomposed, and their coloring matter, slightly changed in its chemical composition, forms rhomboidal or simple needle-shaped crystals. By the addition of water, of ammonia, or some other reagents, it is easy to produce many crystals in a drop of almost any blood, as has been ascertained by Virchow, Kunde, O. Funke, Reichmann, and others. M. Charles Robin has once found in the liver a mass of altered blood as large as a hazel nut, entirely transformed into crystals, or rather containing nothing but hsema-tine crystallized, the other elements of the blood having been absorbed.

Brown-Sequard has pointed out the fact that, in dogs especially, after the extirpation of the supra-renal capsules, the formation of crystals in the blood is very considerable and rapid. 6. Coagulated fibrine. Some micrographers, especially Nasse and Virchow, call certain solid particles floating in the Hood fibrinous flakes. Henle at first considered these particles as shreds of epithelium, from the lining membrane of the blood vessels; afterward us aggregations of cell membranes of destroyed blood disks. Lehmann admits that experiments of Doderlein have proved that these flakes are not composed of coagulated fibrine. Bruch has tried to show that the pretended fibrinous flakes are nothing more than epithelial cells from the skin of the observer himself, which have fallen from his face or his hands on the preparation. It is very probable that these flakes are in a great measure, but not entirely, composed of epithelial cells, and that truly coagulated fibrine, in more or less small particles, exists in blood out of the blood vessels, at least. Besides the morphological elements above described, we find in the blood of certain inferior animals vilriones, or other infusoria, and microscopical drops of fat.

The assumed presence in the blood of another distinct element, i. e., the lymph or chyle corpuscle, has received a different interpretation from that previously admitted: the colorless or pale corpuscles of the blood have been proved to be similar to the chyle or lymph corpuscles. V. Coagulation of the Blood. When drawn from a vein or an artery of man, blood usually begins to coagulate in a few minutes. From the liquid state it passes at first to the condition of a soft jelly, which gradually becomes more and more consistent. The whole mass of the blood seems in the beginning to become solid, but by the contraction of the coagulated substance the liquid is expelled from the kind of network formed by this substance, and the coagulum or clot gradually becomes smaller. The part of the blood which remains liquid is called serum. It had been imagined that the coagulation of the blood depended upon the adhesion of the blood corpuscles one to the other; but it is now well known that the coagulation is only the result of the solidification of the fibrine, which, taking place in the whole mass of the blood, contains the blood corpuscles imprisoned in the network it forms.

The following table shows what changes take place in the blood during coagulation:

The Blood

I. Mammalia.

Long diameter.





Monkeys, from 3624 to.................



Bats, from 4465 to






Bear (Ursus Ameri. canus)............









Cat .



























Red deer.....



Sheep ............



Goat .










Mammalia (continued).

Long diameter.





Guinea pig....


II. Birds.













III. Reptiles.


Tortoise (land)......








IV. Amphibia.


Common frog....



Common toad......















Llq. blood

Liquor sanguinis


C'oag. blood.



Blood corpuscles.........

The serum is the liquor sanguinis deprived of its fibrine, and no longer holding the corpuscles; the clot is the fibrine solidified, and holding the blood corpuscles. It is well proved that the coagulation of the blood, removed from the body, depends upon the coagulation of its fibrine. If blood drawn from the vessels of a living man or animal be whipped with glass rods, its fibrine becomes solidified on these rods, and the whole of it may in this manner be taken away, and then the defibrinated blood remains liquid. Nevertheless, many blood corpuscles sometimes adhere one with another, and in so doing offer a half solid mass at the bottom of the vase, but the least motion shows that there is no coagulation. When they are included in a fibrinous clot, the blood corpuscles contribute to its solidification by some slight adhesion with the fibrine, and by their being included in its network. The circumstances which influence the coagulation of the blood have been the subject of a great many investigations, among which the most important are those of Hewson, John Davy, T. Thackrah, C. Scudamore, Gulliver, and more recently Zimmermann, E. Brticke, and B. W. Richardson. We will examine here only what relates to the principal circumstances and assumed causes of the coagulation of the blood. 1. Influence of temperature.

The coagulation of the blood drawn from the blood vessels does not depend upon the loss of its temperature. It is true that the blood flowing from the vein of a man in a room, even at a summer temperature, soon loses several degrees of heat, and falls from 102° to 98°, or to a lower degree.* But this loss of a few degrees of heat cannot be the cause of the coagulation of the blood, because every day, during the winter, our blood, in the nose, in the ears, and the extremities! of the limbs, loses many more degrees without coagulating. Besides, the blood of cold-blooded animals coagulates as well as that of the warm-blooded. Hewson has demonstrated that it is possible to freeze the blood while yet fluid, and that after being rendered fluid again by thawing, it will coagulate in the ordinary way. Hunter succeeded in freezing the blood in the ear of a living rabit, and after some time, being thawed, it did not coagulate. A low temperature retards coagulation, but the physiologists who maintain that coagulation is prevented by a temperature near the freezing point are mistaken. Brticke says that he has seen blood coagulated at every temperature above 32° F., and even below that point, provided the blood itself was not frozen.

But he has seen the blood of frogs sometimes remain fluid for eight days, while kept in the snow. Brown-Sequard has seen the blood of frogs coagulated so quickly at a temperature of 33° or 34° F., or a little above, that hemorrhage from the section of one third of the ventricular mass of the heart was stopped by a clot, and life was maintained. As a general rule, however, the higher the temperature, within certain limits, the sooner coagulation takes place; but it seems, according to Gulliver, that the coagulating power is lost by a temperature of 150° F., as blood heated to that point remains permanently fluid. The experiments of Polli, Trousseau, Leblanc, and others, seem to show that the temperature most favorable to coagulation is very nearly that of the blood itself. 2. Influence of air. Many physiologists have thought that the cause of the coagulation of the blood, when drawn from the blood vessels of a living man or animal, was a peculiar action of air. Hewson believed that air had a considerable coagulating influence. In proof of this he relates the following experiments: Having laid bare the jugular vein in a living rabbit, he tied it up in three places, and then opened it between two of the ligatures and emptied that part of its blood.

He next blew warm air into the empty vein and put another ligature upon it, and, letting it rest till he thought the air had acquired the same degree of heat as the blood, he then removed the intermediate ligature, and mixed the air with the blood. The air immediately made the blood florid where it was in contact with it, as could be seen through the coats of the vein. In a quarter of an hour he opened the vein and found the blood entirely coagulated; and "as the blood," says Hewson, "could not in this time have been completely congealed by rest alone, the air was probably the cause of its coagulation." Briicke says that air blown in the manner mentioned by Hewson usually hastens coagulation, but that it is not always so. Brown-Sequard has ascertained that blood mixecl with air blown into the jugular veins of dogs does not always coagulate. In some cases, four months after the operation, the blood was found liquid in the vein between two ligatures. It has been remarked that when blood is placed in a cup, coagulation begins sooner in the part in contact with air than in the interior of the liquid, but Briicke states that he has seen coagulation begin as quickly in the surface in contact with the walls of the cup.

If coagulation depended upon a peculiar influence of atmospheric air, it should not take place when blood is not exposed to air. John Davy and H. Nasse have seen coagulation occur as quickly in unexposed as in exposed blood. Scuda-more says even that coagulation is more rapid in a pneumatic receiver, where blood is not submitted to the action of air. From many experiments Briicke has drawn the following conclusions: 1. Air usually hastens the coagulation of the blood. 2. Air, when introduced into the heart and vessels of living turtles, does not induce coagulation. 3. The blood of frogs, when deteriorated by the action of the heart or of the other tissues of the animal, and so deprived of its free oxygen, sometimes requires atmospheric air for its coagulation. 4. Normal blood needs not the presence of air for its coagulation. Therefore, and chiefly from the last conclusion, it follows that air is not the general cause of coagulation of the blood. 3. Influence of carbonic acid. Scudamore admits that blood coagulates out of the body chiefly because it loses its carbonic acid, which in this theory is the substance that in the blood maintains fibrine in a liquid state. Sir Humphry Davy and his brother John made decisive experiments against this view.

They found that blood exposed only to carbonic acid coagulates, though more slowly than when exposed to oxygen. Experiments of Briicke show also that the loss of carbonic acid by the blood is not necessary for its coagulation. 4. Influence of motion and rest. It has been said that blood coagulates out of the body because it is not in motion. If blood received in a bottle is agitated as soon as it flows from the vein, it usually seems to remain liquid; but if carefully examined, a great many particles of coagulated fibrine are found in it. When fibrine coagulates in this case, it cannot form long fibres, disposed in a kind of complicated network in the whole mass of the blood; in consequence of the agitation, it forms only small solid particles. The blood effused in the body, or kept in a blood vessel, between two ligatures, in a living animal, frequently does not coagulate, although it is not in motion. It seems, therefore, that rest is not the cause of coagulation of blood, either in the body after death or out of the living body. 5. John Hunter proposed an absurd theory of the coagulation of the blood; but as he grounds his view on interesting facts, although most of them are only partially true, we shall examine his theory.

He observes: "My opinion is that it (the blood) coagulates from an impression; that is, its fluidity under such circumstances being improper, or no longer necessary, it coagulates to answer now the necessary purpose of solidity." Trying to prove this untenable theory, he says that when the vital principle of the blood is lost, it does not coagulate, which fact, he thinks, shows that coagulation is a vital action. Animals killed by lightning or by electricity, or those which are run very hard and killed in a state of exhaustion, or are run to death, have not their blood coagulated, according to Hunter. He also asserts that blows on the stomach killing immediately, and deaths from sudden gusts of passion, act in the same way, and by the same cause, i. e., the loss of the vital principle. As regards death by electricity, Scudamore and Brown-Sequard have ascertained that blood coagulates after it, but the clot is not so hard as in other cases. Gulliver collected many facts to prove that blood may coagulate in all the circumstances mentioned by Hunter; but in most of these cases coagulation was very imperfect.

It is extremely probable that blood is then altered in its composition, and chiefly in consequence of alterations in the nervous centres and in the muscles. 6. A view proposed by Zimmermann is quite in opposition to that of Hunter. According to the German chemist, blood coagulates because it putrefies when it is not submitted to the chemical influence of living tissues. This view is grounded chiefly on the fact that blood kept liquid by certain salts or other substances becomes at once or very quickly coagulated when a small quantity of putrefied matter is placed in it. This is certainly an interesting experiment, but it does not prove that coagulation depends upon putrefaction, and it seems strange that such a theory should be proposed by a man who knows that sometimes blood coagnlates in two or three minutes after having been drawn from a blood vessel. 7. Dr. B. W. Richardson of London some years ago obtained the great Astley Cooper prize for a paper on the cause of the coagulation of the blood, which he attributes to the separation from the blood of a principle which he thinks always exists in circulating blood. This principle is the carbonate of ammonia.

The proofs of this theory are that the author has always found this substance given out by the blood at the time it coagulates, and that when this substance is kept by the blood it remains liquid. Zimmer-mann has published a paper to show: 1, that the discovery of the constant presence of ammonia in the blood belongs to himself; 2, that there are many facts which are in opposition to the view of Dr. Richardson. These views saem not only improbable, but in opposition to many facts. 8. We come now to the most probable cause of the coagulation of the blood, and the only one which in the present state of science has no fact against it, and seems, on the contrary, to agree with all the facts. This cause is a negative one; it is the absence of a peculiar influence on the blood that, according to the theory, produces, or rather allows coagulation. It is supposed that fibrine naturally tends to coagulate, and that some peculiar influence of the living tissues prevents its doing so. Sir Astley Cooper, Thackrah, and others, have been led to consider this view as probable. They found that blood kept an hour in a vein, between two ligatures, was still fluid, while it coagulated in from two to four minutes when extracted from the vessel.

Gulliver has seen also that blood is very slow to coagulate when confined in a vein of a living dog. Brown-Sequard has found blood still liquid, after many months, in the veins of dogs, where it had been confined after the application of two ligatures, and he has ascertained that this blood coagulated in a few minutes after having been abstracted from the veins. It is well known that blood effused everywhere in the body frequently remains liquid, and also that in leeches it sometimes does not coagulate, while in all these cases as soon as the liquid blood is separated from the living tissues it becomes solid. Coagulation is slow even in the blood vessels and heart of a dead animal or man. But all these facts lead only to the conclusion that a peculiar influence of tissues and organs during life, or a little after death, has the power of preventing coagulation; they do not show what is this peculiar influence. Thackrah thought it was the vital or nervous power of the tissues. Brucke has shown that even when the heart has lost its vital properties, it keeps the blood fluid, and he has arrived at a theory which we do not think yet fully proved.

He maintains that there is no such thing as liquid fibrine in liquid normal blood, and that coagulated fibrine is the result of an atomic change in some part of the albumen of the liquor sanguinis. We will conclude our examination of the facts and theories concerning the cause of the coagulation of the blood, by saying that there is in the blood vessels, and in the heart, and also in other tissues, some physical or chemical influence which maintains the blood fluid, and that when this influence is removed the blood coagulates. Schroeder van der Kolk had imagined that coagulation of the blood was prevented by an influence of the cerebro-spinal nervous centres on the blood through the blood vessels, and he thought he had proved the correctness of this view in finding that when he destroyed the brain and the spinal marrow, coagulation quickly took place in the blood. But Brown-Sequard has found that the destruction of the spinal marrow in the whole length of its lumbar enlargement, in birds and cats, not only did not produce coagulation of the blood, but did not immediately kill the animals, many of which have lived many months after the operation.

When the arteries or veins are changed in their structure by an inflammation or other disease, they lose their power of preventing coagulation. 9. Coagulation is hastened or immediately determined by certain substances. J. Simon has seen it take place on threads kept in the current of blood in veins and arteries in living animals. Dupuy and De Blainville have seen coagulation quickly produced in blood after the injection of cerebral matter. H. Lee has seen the same thing after injection of pus, and Virchow and others after injection of mercury and other substances. Iodine and iodides and galvanic currents hasten coagulation, and have been employed, on account of their influence on blood, for the cure of aneurisms. 10. Coagulation is retarded or entirely prevented by certain substances. Neutral salts act in this way, as well as many medicines and poisons, such as opium, belladonna, aconite, hy-oscyamus, digitalis, strong infusions of tea and coffee, etc. Gulliver has kept horses' blood liquid for 57 weeks by the influence of nitre, and this blood rapidly coagulated when it was diluted with water. This fact explains how in some cases blood does not coagulate in the body after death.

So it is particularly after drowning, or death by irrespirable gases, or poisoning by cyanhydric acid, etc. But if the following fact, mentioned by Polli, be true, it is possible that, in some of those cases where blood has been found fluid in the veins long after death, the coagulation would have been observed taking place at a later period if the blood had been kept long enough. Polli says he has seen blood remain liquid a fortnight and then coagulate spontaneously, and he thinks that blood will always be found to coagulate if kept long enough. 11. The surface of a clot of blood very often presents a more or less considerable layer of coagulated fibrine nearly free from red corpuscles, and consequently without color; this layer is what is called the buffy coat. We owe to Gulliver the explanation of the production of this coat. The red corpuscles have a density superior to that of the liquor sanguinis, and when the blood is at rest they naturally sink until an obstacle prevents their doing so. As long as coagulation has not begun, the globules move toward the bottom of the vessel; and when fibrine forms the solid shreds which constitute the co-agulum, the upper layer of the mass of the blood no more contains red corpuscles, and therefore is colorless.

Now, in inflammation the sinking power of the red globules is increased, so that the colorless layer of coagulated fibrine is thicker than in other cases, and thus it is that the buffy coat and its thickness are sometimes a good indication of the existence and even of the degree of an inflammation. But there are many circumstances besides inflammation and without it which lead to the production of the buffy coat. Andral has shown that when the proportion of red corpuscles is diminished in the blood, the buff exists frequently on the top of a small clot. This is the case in chlorosis, in anemia, etc. Another circumstance which favors the formation of a colorless layer of coagulated fibrine is the aggregation of the red corpuscles in columns or piles (like piles of coin), which renders them heavier and increases their speed in sinking. In inflammation, as shown by H. Nasse, Wharton Jones, and others, the red corpuscles have an increased tendency to aggregate, and this explains why the buffy coat is so frequently thick in inflammation.

Lehmann has shown, however, that all the circumstances which have been considered as favorable to the sinking of the red corpuscles, and to the formation of the buffy coat, are insufficient to explain the facts in all cases, and that there are some unknown causes of production of the buff. 12. The coagulation of blood does not generate heat, as has been imagined. The experiments of John Davy, and especially those of Denis, afford convincing proofs in this respect. VI. Formation of the Blood. We shall not examine here the first formation of this liquid, that is, its production in embryos; this subject belongs to the article Embeyology. We shall only inquire into the sources of the blood, and the mode of production of its principal materials, in completely developed animals. Three sources exist for the formation of the various materials composing the blood: 1, the body; 2, the food; 3, the respiration. That the body itself is a source of blood we cannot doubt. If, as Piorry has shown, we take blood from a dog in su*ch quantity that we cannot abstract one or two ounces more without killing the animal, we find the next day, although the dog has not been fed, that we may take out again 10 or 12 ounces of blood without causing death.

It follows from this fact that a formation of blood has occurred, and, as there has been no food taken, the blood formed must come from the body. As regards the share of respiration in the formation of blood, we shall only remark here that it gives certain gases, especially oxygen. For more details on the influence of oxygen and other gases on the blood, see Respiration. The formation of blood is very rapid when abundant and very nutritive food is taken, as is proved by the following facts, most of which are related by Hal-ler. For several years a young girl was bled sometimes every day, at other times every other day; a hysterical woman was bled 1,020 times in 19 years; another individual had a loss of 1,000 lbs. of blood in a year; in another, 5 lbs. of blood were lost every day for 62 days; a young man had a loss of 75 lbs. of blood in 10 days; an Italian physician, Dr. Cavalli, relates that a woman was bled 3,500 times in 28 years! It seems from these facts, and from many others, that the power of formation of blood increases with the frequency of the losses of this liquid, and with the habit of repairing these losses.

The food, before being able to repair the losses of blood or to give to this liquid the materials which it furnishes to the tissues, must be modified by digestion, and brought to the blood by absorption, either directly or by the lymphatic vessels. The part of the food absorbed by these vessels is called chyle. The transformation of lymph and chyle into blood is an act of much greater magnitude than was formerly supposed. According to the researches of Bidder and Schmidt, there is about 28.6 lbs. of lymph and chyle poured into the blood of a man daily, i. e., from one sixth to one seventh of the weight of the body. Of this amount 6"6 lbs. are true chyle, and 22 lbs. are true lymph. In these two liquids elements similar to those of the blood are found: i. e., water, salts, fats, albumen, fibrine, and corpuscles. This shows that the work of formation of blood from chyle, as well as lymph, is not very considerable; in other words, the transformation of food into blood is already much advanced in the bowels and in the lymphatic vessels. One of the most interesting questions relative to the formation of the blood is that of the origin of the blood corpuscles.

In the first place, as regards the colorless corpuscles of the blood, there is now no doubt that they are entirely similar to the lymph corpuscles, and that they have been brought into the blood with the lymph and chyle. As regards their formation, see Lymph. The source of the albumen of the blood is chiefly the food, and it is brought into the circulation by direct absorption by the veins in the stomach and bowels, and only partly by the chyle. The origin of the fibrine of the blood is not exclusively the food, as some physiologists maintain. It must come from the tissues or from the albuminous matters of the blood, for Brown-Sequard has proved that when blood deprived of fibrine is injected into the arteries of a limb, the veins give out blood containing fibrine, and in greater quantity if the limb is galvanized. Besides, it is known that in animals deprived of food, or bled many times, the quantity of fibrine increases in the blood. There must be a very considerable formation of fibrine in the blood, as, according to the remarks of Brown-Sequard, there are many pounds of this substance transformed into Other substances, in the course of a day, in the liver and the kidneys.

The origin of the fate of the blood, as Persoz, Liebig, Bidder and Schmidt, and others, have well proved, is not exclusively from the fats of the food. But it remains to be shown from what principles of the food or of the blood, and in which organ, the formation of fat takes place. Many of the extractive substances of the blood are either formed in it or in the tissues. As to the salts and the metals of the blood, they come from the food. The sugar of the blood comes in a great measure from the food, and from a transformation of certain substances by the liver. VII. Uses of the Blood. Nutrition - that is, the act by which the various tissues grow or are maintained alive, and by which they excrete materials which are no longer useful to their organization and vital properties - is the result of the interchange between the blood and the tissues. We will now examine how far some elements of the blood may influence the vital properties of the tissues, to show that these properties depend upon some materials furnished by the blood.

Brown-Sequard has discovered that all the nervous and contractile tissues in the brain, the spinal cord, the motor and sensitive nerves, the muscles of animal or organic life, the iris, the skin, etc, may, after having lost their vital properties, their life, recover these properties again, and in some respects be resuscitated, when blood containing a great quantity of oxygen is injected into the arteries of all these parts. Still more, he has found that, when cadaveric or post-mortem rigidity exists in limbs of animals or men, oxygenated blood has the power of restoring local life in these parts. These experiments he has made on many animals, and on the arms of two decapitated men, in one 13, in the other 14 hours after decapitation. He has ascertained that black blood (which contains but a small amount of oxygen) has no power of regenerating the vital properties of the various tissues, and that the more blood corpuscles and oxygen there were in the blood employed, the quicker and the more powerful was its regenerating influence. Blood deprived of fibrine acted as well as blood containing fibrine, showing that fibrine is not a necessary material for the production of the vital properties of the various tissues.

In one case he maintained local life for 41 hours in a limb separated from the body of an animal. For other facts relating to the uses of the blood, see Nutrition, Secretion, and Transfusion; for the circulation of the blood, see Circulation.

* The temperature of the blood is erroneously marked at 9S° on the thermometers. Experiments made by John Davy and by Brown-Sequard have shown that, at least in the abdomen and in the chest, the blood in man is at a higher degree. According to the last-named experimenter, it is between 102° and 103°.