The fat contains 5 per cent. of butyric acid, equal to 6.6 per cent. of butyrin; it is probably very similar to butter fat. After the precipitation of caseine, albumen, lactochrome, and galactine, there yet remain principles precipitable by tannin. As in human milk, the caseine is not readily precipitated but remains suspended in a state of fine division, however far lactic fermentation may have progressed.

§ 126. Milk of the Goat.-The milk of the goat, as a rule, contains more cream than that of the milk of the cow, and rather less albuminous matter.

Its average composition is as follows:

§ 127. Milk of the Mare.-The milk of the mare closely resembles in its constituents the milk of the cow: the caseine, the sugar, and the fat being very similar, if not identical. M. J. Duval asserts that he has discovered in the milk of the mare a new acid, to which he has given the name of equinic, and which crystallises in groups of little needles; it is not volatile without decomposition, in odour fragrant. It is combined with a base volatilised by heat, which the author considers a base of the ammonia type. Its reactions with silver nitrate, ferric chloride and auric chloride distinguish it from hippuric acid. No analyses are, however, given.

The mean composition of mare's milk is as follows:

MILK OF OTHER MAMMALS; LACTESCENT PRODUCTS OF BIRDS AND PLANTS.

The following Notes on the Composition of the Milk of other Mammals, &c., may be found useful for comparative purposes.

§ 128. Milk of the Sheep.-Sheeps' milk is remarkable for its high specific gravity, and the large amount of solid matter which it contains; the specific gravity ranges from 1038 to 1041, and the total solids may rise as high as 19 per cent. The average composition is as follows:

The caseine behaves similarly to the caseine of cows' milk, and separates easily by dilution, acidulation with acetic acid, &c. (see p. 241.) The fat yields 5 per cent. of its weight of butyric acid, and is probably of similar composition to the milk-fat from cows' milk.

§ 129. The Milk of the Camel.-Chatin has analysed the milk of the camel. He describes it as perfectly white in colour, and possessing globules smaller but more numerous than those in cows' milk, the diameter being on an average one-half. Specific gravity, 1.042. It appears to be rather richer in milk-sugar and caseine than cows' milk. Dragendorff+ has also analysed camels' milk, and gives the following figures:

§ 130. Milk of the Llama.-Doyére‡ has analysed the milk of the llama. The mean of his three analyses is as follows:

Milk-fat,
Albuminoids,

Milk-sugar,
Ash,
Water,

Per cent.
3.15

.90 5.60

.80

89.55

§ 131. Milk of the Hippopotamus.-There are few opportunities of analysing

Sur le Lait de la Chamelle à deux Bosses, par. M. Chatin. Journal de Pharmacie et Chemie, t. i., 4 ser., p. 264.

+ Zeitschrift f. Chemie, 1865, s. 735. Ann. de l'Inst. Agrom. 1852, p. 251.

the milk of this enormous animal, as it is fierce when it suckles its offspring. A sample of the milk was, however, investigated by Gunning.* He describes it as of an acid reaction, and under the microscope showing larger globules than that of other animals. The young hippopotamus sucks under water, and can remain there for a much longer time than the adult animal. The secretion of milk is excessive in quantity, and escapes from the distended teats in streams, which make the water around the animal quite opaque. Its general composition appears to be as follows:

Per cent.

4.51

4.40

•11

90.98

§ 132. Milk of the Sow.-The mean of eight analyses collected by Königt of sow's milk, is as follows:

:

Per cent.

4.55

7.23

3.13

1.05

84.04

15.90 11:41

There are also two analyses of the milk of a sow investigated by Filhol and Joly; the animal was fed on horse-flesh, a diet far from natural; under this diet was secreted a highly albuminous fluid, containing but little sugar. Specific gravity 1·044.

Per cent.

$133. Milk of the Bitch.-The milk of the bitch is highly charged with albuminous solids, and is of a specific gravity ranging from 1034 to 1'036. It has been investigated by Simon, Dumas, Filhol and Jolly, Talmatescheff, Bensch, Scubotin, and others, with the following mean results :

§ 134. Milk of the Cat.-The milk of the carnivora generally has the peculiarity of having the milk-sugar almost entirely replaced by lactic acid, and hence the milk invariably possesses an acid reaction. An analysis of the milk of a cat by Commaille is as follows. The milk was taken twenty-four hours after kittening; it was feebly acid :—

The 467 would correspond to about 25 of galactine.

§ 135. Milk-like Secretions of Birds and Plants.-It is usually held that mammals alone secrete milk, but this is by no means certain; for during the latter portion of the incubation-period, as well as more profusely for a little while after the young birds are hatched, the pigeon secretes a nutritious albuminous fluid in her crop, which is supposed to be used for the purpose of feeding the young birds. According to Lecomte's analysis this secretion contains,

Caseine and salts,

23.23

10:47

66.30

Such milk-like secretions are by no means confined to the internal mucous membranes of birds. Jonge has made a most valuable research on the secretion of the glands known to anatomists as Glandula urophygii, situated at the tail of the common goose. The secretion was obtained in sufficient quantity for a complete qualitative and quantitative analysis, and although the analysis was not quite so complete as if a larger quantity had been obtainable, it fairly shows that there is a considerable analogy between milk and this secretion, the most marked difference being that no trace of milk-sugar could be found. The analyses of two samples were as follows:—

* "Ueber das Secret der Talgdrüsen der Vögel und sein Verhältniss zu den fetthaltigen Hautsecreten der Saugthiere, insbesondere der Milch," Von D. de Jonge. Zeitschrift für Physiol. Chemie, Von F. HoppeSeyler. Strasburg, 1879.

In the vegetable kingdom, numbers of trees or plants yield a white fatty secretion, popularly called milk, though, as a rule, such fluids have no right to this title, being totally different in composition and properties. A very remarkable exception to this assertion is, however, met with in the "milk tree" (Brosimum galactrodendron), to be found in Central America. This tree, on incision, yields an abundance of a thickish feebly acid fluid, coagulating on exposure to the air. M. Boussingault has recently analysed this juice, and considers it perfectly analogous to ordinary milk, since it contains a fatty principle, an albuminous principle, a sugar, and phosphates. The exact composition of these different matters has, however, not been determined. Boussingault's general analysis is as follows :

This milk is used largely as a food in the regions where the tree grows.

ABNORMAL MILKS.

§ 136. Milk which deviates from the natural secretion, the animal suffering from no disease, and milk secreted under unnatural conditions, may be conveniently classed as "abnormal." (Milk derived from the unhealthy will be considered in another section.) Instances of healthy cows giving milk differing essentially from ordinary milk are very few. One such, however, is recorded by Mr. Pattinson, who analysed the milk of a roan cow, which only gave 2 per cent. of albuminoids, and yielded no less than 4 grms. per litre of common salt. The animal is stated to have been in good health.

The newly-born human infant almost constantly secretes a fluid in the mammæ, and adult males have not only secreted milk, but that in abunGance enough to suckle. Females also, both human and animal, occasionally secrete milk without having been previously pregnant. With regard to the milk secreted by infants, there is some doubt about its real nature. Kölliker does not view it as a true milk, but considers its appearance connected with the formation of the mammary glands. Sinety, on the other hand, upon anatomical grounds, considers it a true lacteal secretion. It probably is a sort of imperfect milk loaded with leucocytes, and this is the more likely, as Billard (Traité des Maladies des Enfants nouveau nés, 3me edition, 1837, p. 717) notices that it frequently ends in abscess.

Schlossberger gives an imperfect quantitative analysis of a sample of