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 hotu"s 

 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 



