4 MILK 
animal, and a faint sweet taste. The opacity 
is due largely but not entirely to the fat globules. 
The reaction of freshly drawn milk to litmus is 
usually alkaline, but is sometimes amphoteric; 
that is, it turns the red paper blue and the blue 
paper red. The sp. gr. varies between 1.027 
and 1.035. It usually undergoes a gradual 
augmentation (sometimes termed Recknagel’s 
phenomenon) for a considerable time after the 
sample has been drawn. The increase may 
amount to two units (water being 1000). The 
sp. gr. becomes stationary in about five hours 
if the milk is maintained at a temperature 
below 15°, but at a higher temperature it may 
require twenty-four hours to acquire constancy. 
The change is not entirely dependent on the 
escape of gases. 
Unless collected with special care and under 
conditions of extreme cleanliness, milk always 
contains many bacteria, animal matter of an 
offensive character, such as epithelium, blood 
and pus cells, particles of feces, and soil. 
At ordinary temperature milk soon undergoes 
decomposition, by which the milk sugar is 
converted principally into lactic acid, and the 
proteins partly decomposed and partly coagu- 
lated. The liquid becomes sour and the fat is 
inclosed in the coagulated casein. In the initial 
stages of decomposition the proteins frequently 
