VARIATIONS OF AIILK CONSTITUENTS 



167 



These results show a remarkable uniformity in the 

 ratio of fat to casein throughout the lactation period. 

 The ratio remains quite constant for seven or eight 

 months and then increases slightly, remaining the 

 same during the rest of the lactation period. 



It will be of practical interest in this connection to 

 observe what the relation of fat and casein is during 

 the season in the case of the mixed milk of many 

 herds of cows, as obtained at New York cheese fac- 

 tories 



RELATION OF FAT AND CASEIN IN CHEESE-FACTORY 



MILK DURING SEASON 



Month 



April 



May 



June 



July 



August . . . . 

 September, 

 October. . . 



Per cent 

 of fat 



3.43 

 3.58 

 3.64 

 3.62 

 3.84 

 3.92 

 4.23 



Per cent 

 of casein 



2.29 

 2.34 

 2.47 

 2.43 

 2.39 

 2.55 

 2.81 



Parts of casein for 

 one part of fat 



Fat : Casein 



1: 0.67 

 1:0.65 

 1: 0.68 

 1:0.67 

 It 0.62 

 1: 0.65 

 It 0.66 



The same fairly uniform relation holds except in 

 the case of the month of August, when the casein 

 decreased relative to fat. It is interesting to notice 

 how closely the relation of fat and casein in cheese- 

 factory milk agrees with that of the Holstein-Friesian 

 and Ayrshire types as given in the table on p. 165. 

 The cheese-factory cows were grade Holsteins and 

 Ayrshires to a considerable extent 



Influence of fresh pastures and of drouth upon 

 the relation of fat and casein in milk. — Usine the 

 data already given, we have the following tabular 



