6 CITY MILK SUPPLY 



The ordinances of boards of health prohibit the use of colostrum by for- 

 bidding the sale of milk for a considerable period before and after calving. 



TABLE 5. CHANGE OF COLOSTRUM TO NORMAL MILK (HOUDET) 



Color of Milk. Milk is a yellowish-white opaque fluid having a 

 slightly acid reaction to phenolphthalein and an amphoteric reaction to 

 litmus; it is of sweet taste and of indefinable characteristic odor. The 

 yellow color is derived from the fat globules and varies greatly in the 

 milk of different breeds and also in the milk of the same cow at different 

 seasons, generally being paler during the winter months and of greater 

 intensity soon after the cow is put on pasture. By feeding experiments 

 Palmer and Eckles proved that milk owes its color principally to carotin 

 but also to xanthophylls. These pigments are not built up in the cow's 

 body but are merely taken up in the food and subsequently secreted in 

 the butterfat. In thin films, especially after skimming, milk has a 

 bluish tinge but the blueness is not true color being rather in the nature of 

 opalescence caused by tiny particles of phosphate of lime that remain 

 undissolved in the milk plasma. 



Opacity of Milk. The opacity of milk is due to the casein interfering 

 with the passage of light through the fluid. 



Specific Gravity of Milk. The specific gravity of the milk of indi- 

 vidual cows, at 60F. varies from 1.0135 to 1.0397 but in the mixed 

 milk of a herd, rarely falls outside the limits 1.0130 to 1.034. Since 

 butterfat is lighter than water, its increase lowers the specific gravity 

 whereas an increase in the solids-not-fat, raises it. Hence skimming 

 milk increases its specific gravity and watering lowers it. Consequently, 

 taking the specific gravity is widely practised to detect this sort of tamper- 

 ing. As the milk may be manipulated to pass the test it serves merely 

 as an indication. The test is usually made with a lactometer, of which 

 there are two kinds, the Quevenne and the New York Board of Health, 

 in common use in the United States. The latter is used less generally 

 than the former. 



