Carbon. Hydrogen. Nitrogen. Oxygen. Iron and Salts.

712 ... 1130 ... 214 ... 245 ... 2

The coloured corpuscles of the blood are constantly undergoing destruction, whilst new ones take the place of those that disappear. If such a renewal did not occur, every large loss of blood would inflict permanent injury on the animal, whereas experience shows that recovery soon takes place, even from abundant hemorrhage, temporary weakness being followed by perfect restoration to health and strength. As much as a gallon of blood may be withdrawn from the veins of a horse every month for several months together without impairing its health. The seats of formation, or the factories as they may be called, of the coloured corpuscles, appear to be the absorbent glands and their tributaries; the cancellous or spongy tissue in the heads of the long bones; the liver; spleen; thymus and thyroid bodies, and the gland-like tissue forming the sub-mucous coat of the alimentary canal. This difference in their place of origin may account for minor differences observed in the size, form, and colour of both the red and the white corpuscles. As the red corpuscles grow old they seem to enlarge, to lose their coloured contents, and either to break up in the vessels or to be seized upon in the spleen or other organ and consumed by large colourless cells named phagocytes.

Additional reasons for believing that their term of life is not a long one are, first, because great numbers of colourless corpuscles, some of which become coloured, are added to the blood after every meal; and, secondly, because if the blood of one animal be injected into the vessels of another, the corpuscles, if capable of being distinguished, do not long persist in their new host.

Crystals of Haemoglobin.

Fig. 185. - Crystals of Haemoglobin.

The white or colourless corpuscles, named also leucocytes and lymphocytes, are present in the blood in much smaller number than the red. The proportion that they have to each other is not, however, a constant one, owing to the fact just stated, that a large accession to the numbers of the white corpuscles occurs after every meal. In the fasting state there is about one white corpuscle to every fifteen hundred red corpuscles, whilst after food the proportion may rise to one white to three hundred red, or even higher. Perhaps, taking the average, the proportion is about 1:500 or 1:1000.

The white corpuscles are spheroidal in form, clotted or granular in aspect, the granules they contain being in some instances coarse, in others fine, indicating in all probability a difference in their place of origin. By the action of various chemical substances a nucleus is brought into view, and sometimes two or three appear with great distinctness. Their diameter is about 1/2500 inich. Their most remarkable character is the power they possess of undergoing changes of form and of moving from place to place (fig. 186). They act, in fact, as if they were parasites, living in the blood, but not necessarily confined to that medium. If a drop of blood be received upon the warmed stage of a microscope, and evaporation be prevented, they may be seen to exhibit perfectly independent movements, thrusting out little processes in this or that direction and withdrawing them again, exactly as an amceba would do if placed under the same conditions. By this means they are able to pass through the walls of the smaller blood-vessels and then wander freely through the outlying tissues, a process that is termed diapedesis.

The small corpuscles known as platelets are flattened, disc-shaped, or irregular particles, in regard to the nature of which little has been ascertained.

The plasma of the blood, in which the corpuscles are suspended, is a clear fluid having a specific gravity a little less than that of the corpuscles, which, therefore, when the blood is at rest, have a tendency to fall to the bottom of the vessel. It contains a large proportion of nutritive material in the form of albuminous constituents, amongst which fibrinogen, serum-globulin, and serum-albumin are the most important, and it is also the solvent of many other bodies on their way to the tissues, or which result from the decay and disintegration of the various organs. Thus sugar, fats, urea, uric and hippuric acids, cholesterin and lecithin, and many salts are constant constituents. The following table shows the results obtained from the analysis of the blood-plasma of the horse by two excellent chemists, No. I being the result obtained by Professor Hoppe Seyler and No. II that of Professor Hammarsten.

Colourless Blood Corpuscles, showing successive changes of outline during a period of ten minutes.

Fig. 186. - Colourless Blood Corpuscles, showing successive changes of outline during a period of ten minutes.

Hoppe Seyler only examined the blood-plasma of one horse; Professor Hammarsten of three, of which he took the mean.

No. I.

No. II.

Water...

.. 908.4

917.6

Solids ...........

91.6

82.4

Total albuminous bodies

77.6

69.5

Fibrin...

10.1

6.5

Globulin...

-

..... 38.4

Serum albumin

-

24.6

Fat ............

1.2

12.9

Extractives ...

4

Soluble salts ...

6.4

Insoluble salts...

1.7