44 MILK HYGIENE 



lose and salts) is far less variable. This applies espe- 

 cially to lactose, which seldom shows the given mini- 

 mum and maximum percentage. In the detection of 

 adulterations, the percentage of lactose furnishes, there- 

 fore, a better guide than the percentage of fat. 



By mixing the milk of the members of a herd, the 

 individual variations in composition are more or less 

 equalized, so the composition of the whole quantity 

 approaches the average for cow's milk. There are, 

 however, some herds in the milk of which the percent- 

 age of fat is much higher than in others ; this is a matter 

 of selection or of breed, so, of course, the composition 

 of milk of separate herds will not be the same. As cows 

 usually calve at certain seasons the number of fresh 

 cows and old milkers is not the same at all seasons and, 

 for this reason^ the composition of the milk changes. 

 We have the following figures showing the average per- 

 centage of fat as found upon daily analyses of milk 

 from three large herds. 



February May August November 



a. 3.18 3.42 3.61 3.47 



6. 3.69 3.56 3.64 3.77 



c. 3.03 3.38 3.51 3.32 



In herds a and c, particularly, calving is distributed 

 unevenly, which causes the percentage of fat to be 0.5 

 per cent, lower in winter than in summer. 



Many of the external influences that have been men- 

 tioned as applying to the individual animal and that 

 result in a temporary change in the composition of the 

 milk, may apply, at the same time, to all of the animals 

 in a herd and thereby influence the fat content of the 

 herd milk. This is seen when there is a change of food, 

 disturbance in the stable, storms, extreme heat and so 

 on. However, variations in the composition of the entire 

 quantity of milk caused in such ways are, in most cases, 



