. The physiology of domestic animals ... Physiology, Comparative; Veterinary physiology. MAMMAKY SECEETION. 611 entirely of fat, and are composed of combinations of glycerin with oleic, palmitic, and stearic acids. They are surrounded b}r a thin layer of casein, not in the form of a solid deposition, but the casein probably exists in a condition of high imbibition rather than in a state of solidity or of true solution. The layer of casein cannot be regarded as consti- tuting a membrane, although it, to a certain extent, fulfills the same function. If acetic acid is added to a preparation of mi
. The physiology of domestic animals ... Physiology, Comparative; Veterinary physiology. MAMMAKY SECEETION. 611 entirely of fat, and are composed of combinations of glycerin with oleic, palmitic, and stearic acids. They are surrounded b}r a thin layer of casein, not in the form of a solid deposition, but the casein probably exists in a condition of high imbibition rather than in a state of solidity or of true solution. The layer of casein cannot be regarded as consti- tuting a membrane, although it, to a certain extent, fulfills the same function. If acetic acid is added to a preparation of milk, under the microscope it will be seen that the caseous envelope is dissolved and the oil-globules run together and form irregular masses of oil. When cows' milk is shaken up with caustic potash and then agitated with ether the oil passes into solution in the ether. The previous subjection to the action of caustic potash is, however, essential, since ether will not dissolve the oil from cows' milk unless the casein envelopes be previously dissolved by acetic acid or Fig. 258.—Microscopic Appearance op Milk and Colostrum. (Landois.) The upper half of the figure represents milk; the lower half colostrum. If milk be allowed to stand for some time the oil-globules, which in freshly secreted milk are uniformly distributed through the milk, now rise to the surface and form a layer largely composed of fat, or the so-called cream. The reaction of freshly secreted milk is alkaline in the herbivora and in the human female, while that of the carnivora is acid. The milk of herbivora frequently will exhibit both an alkaline and an acid reaction, clue to the presence of an acid sodium phosphate (H2TSTAP04) and of an alkaline disodic phosphate (NA2HP04). Such a reaction is spoken of as amphioter. When milk is allowed to stand, the alkaline reaction, when present, gives place to an acid reaction, which is clue to the fermentation of the milk-sugar and its conversion into lactic ac
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