14 GENERAL CONDITIONS AFFECTING BACTERIA IN MILK 



of the latter is easily broken up, more apt to produce oil drops on 

 the top of the vessel, and is not so easily restored. These 

 facts are of importance in relation to the transportation of 

 milk and the examination of milks and cream from transported 

 cows.^ 



The following table may be added as an illustration of 

 chemical differences in the milk composition of various herds 

 of cattle : — 



A somewhat similar table has been constructed by Droop 

 Richmond, and is as follows : — 



(2) The period of lactation. — Age per- se exerts a certain influence 

 upon the quality of the milk. A cow not only arrives at a time of 

 maximum yield as regards quantity of milk, but also as regards 

 quality. Yet a finer distinction may be drawn, for the quality 

 undergoes considerable change according to the period of time 

 which has elapsed since calving. There is, as referred to above, 



^ For American breeds of dairy cattle and their chief distinguishing char- 

 acteristics, see U.S. Dep. of Agriculture, Fifteenth Ann. Rep. Bureau of Animal 

 Industry, 1898, pp. 136-200. 



