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COW’S MILK. 645
Perfectly fresh amphoteric milk does not coagulate on boiling, but
forms a pellicle consisting of coagulated casein and lime-salts, which
rapidly re-forms after being removed. After a sufficiently strong spon-
taneous formation of acid it coagulates on boiling, and lastly, when the
formation of lactic acid is sufficient, it coagulates spontaneously at the
ordinary temperature, forming a solid mass. It may also happen, espe-
cially in the warmth, that the casein-clot contracts and a yellowish or
yellowish-green acid liquid (acid whey) separates.
Milk may undergo various fermentations. Lactic-acid fermentation, brought
about by Huppe’s lactie-acid bacillus and also other varieties, takes first place.
In the spontaneous souring of milk we generally consider the formation of lactic
acid as the most essential product, but a formation of succinic acid may also take
place, and in certain bacterial decompositions of milk, succinic acid and no lactic
acid is formed. The materials from which these two acids are formed are lactose
and lactophosphocarnic acid. Besides the lactic acids, the optically inactive
as well as the dcxtro and levo acids, and succinic acid, volatile fatty acids, such
as acetic acid, butyric acid, and others, may be formed in the bacterial decompo-
sition of milk.
Milk sometimes undergoes a peculiar kind of coagulation, being converted
into a thick, ropy, slimy mass (thick milk). This conversion depends upon a
peculiar change in which the milk-sugar is made to undergo a slimy transforma-
tion. This transformation, which requires further investigation, is caused by
special micro-organisms.
If the milk is sterilized by heating, and contact with micro-organisms
prevented, the formation of lactic acid may be entirely stopped. The
production of acid may also be prevented, at least for sometime, by many
antiseptics, such as salicylic acid, thymol, boric acid, and other bodies.
If freshly drawn amphoteric milk is treated with rennet, it coagulates
quickly, especially at the temperature of the body, to a solid mass (curd)
from which a yellowish fluid (sweet whey) is gradually pressed out. This
coagulation occurs without any change in the reaction of the milk, and
therefore it is distinct from the acid coagulation.
In cow’s milk we find as form-elements a few colostrum corpuscles
{see Colostrum) and a few pale nucleated cells. The number of these
form-elements is very small compared with the immense amount of the
most essential form-constituents, the milk-globules.
The Milk-globules. These consist of extremely small drops of fat
whose number is, according to Woll,1
1.06-5.75 millions in 1 c.mm.,
and whose diameter is 0.0024-0.0046 mm. and 0.0037 mm. as an average
for different kinds of animals. It is unquestionable that the milk-globules
contain fat, and we consider it as positive that all the milk-fat exists in
them. Another disputed question is whether the milk-globules consist
entirely of fat or whether they also contain protein.
^n the Conditions Influencing the Number and Size of Fat-globules in Cow’s
Milk, Wisconsin Exp. Station, 6, 1892.
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