Milk, the liquid secreted by the mammary glands of female mammals. Its color is generally yellowish white, but sometimes bluish white, and it is quite opaque. Its specific gravity, according to Scherer, varies from l.018 to 1.045. According to Simon, the average specific gravity of human milk is 1.032. There is a difference of opinion among chemists as to whether normal milk has an acid or an alkaline reaction. According to Berzelius, Peligot, and Lassaigne, it is acid; Simon and others regard it as alkaline, and attribute the acid reaction found by others to its having acquired acidity by standing, or to disease. Numerous examinations, however, seem to indicate that healthy milk may he alkaline, neutral, or acid, according to the food of the animal. D'Arat and Petit say that the milk of stall-fed animals is always acid, and becomes alkaline only when they are turned out to grass. Hermhstadt found milk that had remained long in the udder acid. Fraas had a cow milked six times a day, and found the milk at each time feebly alkaline. After an interval of 24 hours she was again milked, when the first portion of the milk was found alkaline and the last portion acid.
The opacity of milk depends upon numerous yellow microscopic globules of a fatty substance from 1/12,000 to 1/3000 of an inch in diameter, shown in fig. 1. According to Chevreul, cow's butter is composed of stearine, margarine, and oleine, with small quantities of buty-rine, caproine, and caprine; but late analyses by Heintz and others deny the existence of margarine, saying that it consists of palmatine and a small quantity of stearine, together with small quantities of glycerides, yielding by saponification myris-tic and butic acids. (See Butter.) In regard to the size of the butter globules observers differ. Dr. Carpenter gives their diameter as 1/12,700 to 1/30400 Dr.Dunglison adopts this measure. Dr. Dalton says: "The largest of the globules are not over 1/2000 the greatest number of them being about 1/10,000 of an inch in diameter." According to Dr. Bennett, their diameter varies from 1/2500 to 1/1500 of an inch. Ihere has recently been considerable discussion as to the existence of an envelope, or "membrane" as some term it, around the globules. Dr. Von Baumhauer and F. Knapp assert that they have none, and others concur with them. Dr. Bennett and others maintain that either a caseous or an albuminous enve-lope exists, and experiments are cited as sustaining this opinion.
The taste of milk is bland and sweetish, and it has a peculiar animal odor, depending somewhat upon the animal, but perhaps still more upon the food. Gar-lic even if the plant is partaken of in very small quantities, is distinctly perceptible by the smell as well as by the taste. Milk has always been an article of man's diet, and forms the entire nourishment of the early existence of all mammals; and it contains all the elements necessary for the growth of the animal framework. - In comparing milk of the same animal under different conditions of age, health, food, length of time after parturition, etc, as remarkable differences in the proportions of the ingredients will be observed as when samples of the average milk of several different species of mammalia are compared. The following table exhibits the composition of several kinds of milk, the first column presenting the average result of ten analyses by Prof. Poggiale, the next four being furnished by Messrs. Henri and Chevalier in the Journal de Pharmacie vol. xxv., and the last by Dr. Samuel R. Percy of New York as the composition of the milk of a healthy woman.
The albumen in these analyses is reckoned with the caseine.
Sugar of milk..
An analysis by Volcker is given in the article Cheese, and also one of the cheese made from the milk. Of these constituents the most uniform in its proportions is the sugar, but this may be materially increased by the use of saccharine food, as is found in feeding cows upon carrots and beets. The sugar of milk is crys-tallizable, but it is less sweet and less soluble in water than cane sugar. Milk from unhealthy animals often exhibits an increased proportion of phosphate of lime in the ash. When milk is exposed to a warm temperature it ferments, and lactic acid is generated, which has the same ultimate composition as sugar of milk. Under certain conditions the vinous fermentation may now take place, the sugar of milk be converted into grape sugar, and a spirituous liquor be produced, as is practised by the Tartars. (See Kumiss.) Various circumstances affect the quality and composition of milk. That called colostrum, given by the cow immediately after calving, is yellowish, thick, and stringy; for several days it is unfit for use. Examined by the microscope, it is seen to contain numerous large and granular corpuscles.
Milk drawn from the cow in the morning is thought to be better than that of the afternoon; and a remarkable difference is perceived in the proportion of cream in the first and last portions of the milking, the latter containing twice as much cream as the same quantity of milk of the former. In the udder of the cow the cream seems to rise as it does when the milk is collected in a vessel. - Some of the methods of testing the quality of milk are noticed under Galactom-eter. By this the specific gravity is ascertained both of the whole milk and skimmed milk; but as these data are of little value without a knowledge of the proportion of cream, another instrument, invented by Sir Joseph Banks, and called the lactometer, is used in connection with the galactometer. It is a tube about 1/2 in. in diameter, and 10 in. of its length graduated in tenths of an inch. When tilled with milk, the tube is set aside for 12 hours for the cream to rise. The proportion of this is then read off in the number of divisions occupied by the upper stratum. The thickness of this stratum is very variable with different sorts of genuine milk; but its general range is from 9 .to 14 of the divisions, indicating as many percentages. Dr. Hassall thinks the- average of pure milk does not exceed 9 1/2 of cream.
Dr. Normandy rates it at 8 to 8 1/2 The proportion of cream is also determined by an instrument invented by M. Donne of Paris, called the lactoscope, the principle of which is based upon the opacity of the fluid caused by the buttery particles. A few drops of the milk are introduced between two plates of glass, so set in an ocular tube that they can be brought close together or separated by means of a graduated screw, and thus enclose at their base a thinner or thicker stratum of milk. The observer then looks through the tube at a light set 3 ft. off, and gradually separates the plates of glass, increasing the depth of the layer of milk, till this at last becomes so opaque that the light is lost to view. The figure to which an index on the instrument then points refers to a table, upon which the corresponding quality of the milk as to quantity of cream is designated. As the large globules of cream are the first to rise, if this is removed the remaining skim milk will contain only the smaller globules'; and this has been used in Germany as a means of ascertaining whether milk has been skimmed. - Milk is easily adulterated by substituting various cheap materials for the natural ingredients, thereby seriously affecting its quality, while the fraud can be detected only by the skilful examination of the chemist.
The nourishing cream is removed and water is substituted. This involves the addition of white thickening substances to disguise the cheat, and of other strange ingredients to restore or retain the sweetness and saltness of the milk. Large cities are almost hopelessly exposed to these frauds; but worse than all, a large portion of the milk with which they are supplied is that of diseased cows kept in crowded stables and fed with cheap unwholesome food, especially the swill of distilleries. The evil became so serious that several years ago the attention of medical men in New York was directed to the subject, and in 1859 a careful investigation was made into the character and properties of the milk of cows fed upon the swill of distilleries, the results of which are embodied in a report of S. R. Percv, M. D., and published in the "Transactions" of the New York Academy of Medicine," vol. ii., part iv. The following are some of the analyses of healthy and diseased milk in that report:
No. 1 is the milk of a cow kept for family use in New York; No. 2, of swill-fed cows from distillery stables in New York; both the analyses are by Dr. Doremus. The following are by Dr. Percy: No. 3, country milk furnished by a dealer to customers in New York; No. 4, milk as drawn from the cows in a Brooklyn distillery stable; No. 5, sample of same delivered to customers; No. 6, another sample of the same as sold to customers; No. 7, milk from a sick cow, Brooklyn distillery stables; No. 8, sample of the milk used by Gail Borden for preparing the "condensed milk." Healthy milk was observed by Dr. Percy to have an alkaline reaction, while that from diseased animals was always acid. The same observation had been made by Gay-Lussac, Berzelius, and others; and the effect is found to be induced in a short time in animals shut out from the light of day, and in those confined in bad air and supplied with bad food. In the analyses, the bad milk is at once recognized by its unduly large proportion of caseine, while the sugar and often the butter is as disproportionately small. The large amount of saline matter found in bad milk is caused by the addition of salt made for the purpose of disguising the adulteration with water.
But the proportions of the ingredients, though sufficient to expose the character of the milk, cannot indicate the poisonous qualities of the worst sorts, nor the evil effects that may follow their use. In organic compounds, such as we use for food, as in the air we breathe, the most dangerous poisons may lie concealed beyond the power of detection of the most delicate tests or the most powerful microscopes, and their existence is brought to light only by their effects upon the human system. Thus the real nature of the distillery milk is most properly shown in the report by citation of several cases of disease in young children traced directly to its use. - Milk may be impure from natural as well as artificial causes. The microscope affords a pretty good test m both cases, starch granules and chalky particles be-in" easily detected, the latter especially on the addition of a little acid. The simplest cases of diseased milk are those caused by feverishness in the cow. This causes the globules to assemble in groups, as if they possessed a certain degree of vitality somewhat resembling that of blood globules. Fig. 2 shows the microscopic appearance of the globules in feverish milk.
Fig. 3 gives the appearance of a sample of milk from a distillery stable in Brooklyn, examined by Dr. Percy. It was taken from a cow very ill with high fever and inflammation of the bow-els. The milk was scanty and blue, and contained, in addition to the broken-down butter globules and spores of conferva?, blood globules which are not shown in the drawing. Fig. 4 is a sample of the same milk after standing closely corked for 24 hours. The spores of confervas have grown to perfect plants, with branching stems. These drawings were given in the "Report of the New York State Medical Society" for 1860. - Prof. James Law of Cornell university has made some investigations in relation to fungi in cows' milk, of much practical interest. Pie arrived at the conclusion that several of the low forms of vegetable life were introduced into the water of which the cows drank, as he found the same forms in the water and also in the blood of the animals. The experiments were made in such a manner as to preclude the possibility of the introduction of the organisms from any other source.
The details are given in a pamphlet reprinted from the "Lens," and also in an address on poison cheese before the American dairyman's association in 1872 by L. B. Arnold of Ithaca, N. Y. Prof. Gerlacli of Hanover has recently made a series of investigations in regard to the effect of a diet of milk from tuberculous cows, which would lead to the conclusion that tuberculosis may be transmitted in this manner from the bovine to the human race. The subject is at the present time undergoing examination in this country, but no conclusive results have vet (January, 1875) been arrived at. - The preservation of milk from putrefaction is an object of no little importance. In France this is accomplished by causing the solid portion of the milk to combine with other matters, and thus separate m a solid form from the aqueous portion; but the compound is not properly milk. It is also evaporated down to the consistency of sirup, and then by the addition of sugar made into a solid compound of milk and sugar; and by a third method it is preserved by expelling the air from it, and hermetically sealing the bottles while they are under a steam heat of about 100° 0. In this way milk has been preserved perfectly fresh for 5 1/2 years.
In the United States a patent was granted in 1856 to Gail Borden, jr., for another method, which he successfully conducted in Litchfield co., Conn., and afterward in Texas, supplying what is called " condensed milk " to consumers throughout the country. By his process the milk when drawn from the cow is immediately cooled to about 60° F., in order to check its changing. It is soon after rapidly heated in a vat surrounded with hot water to 180° or 190°, when refined white sugar is added in the proportion of about one part to nine of milk. It is kept in the hot water vat about 30 minutes after adding the sugar, and is then removed to vacuum pans in which evaporation of the water is effected at a temperature not exceeding 160°. When it is sufficiently concentrated, the pans are quickly cooled down by passing cold water in the place of steam through the heating pipes. The milk, converted into a paste, can then be removed from the pans without adhering to their sides. Another preparation, known as " solidified milk," is also made by a process like one of the French methods above referred to. To 112 lbs. of fresh milk 28 lbs. of sugar are added, together with a teaspoonful of bicarbonate of soda, merely enough to neutralize any slight acidity.
The mixture is then evaporated by the heat of a water bath carefully regulated, and the process is hastened by a current of air made to pass over the surface. An apparatus is kept in operation gently stirring the mixture during the evaporating process, until at last the milk and sugar are reduced to a creamy-looking powder. This when cooled in the air is weighed out into pound parcels, and compressed by machinery into the shape and size of small bricks. These, covered with tin foil, are ready for sale, and are well adapted either for preservation during long voyages or for immediate domestic use. The preparation of condensed milk is conducted upon a large scale in Switzerland.
Fig. 4. - Sugar Of Milk.