IO 



MILK AND ITS HYGIENIC RELATIONS 



authors regarding the average composition of cows' milk. Much 

 information upon this subject will be found in numerous text-books. 

 The variations found in the composition of different milk 

 samples is well illustrated by the figures obtained by Kirchner, 

 who gives the range in percentage composition of the samples 

 examined : 



Water . 



Fat 



Caseinogen . 



Albumin 



Lacto-protein 



Lactose 



Ash 



from 83-90 

 0-8-8-0 



2-0-4-5 



0-2-0-8 

 0-08-0-35 

 3-0-6-0 

 0-6-0-9 



These results show the impossibility of adopting any set of 

 figures as a standard for the composition of cows' milk. Doubtless 

 some of the extreme figures are attributable to certain causes 

 which are considered below. 



The average composition of cows' milk is affected by the breed 

 of the cow, although the individual variations which occur between 

 the composition of the milk of different cows of the same breed are 

 sometimes as great as those which may reasonably be attributed to the 

 breed of the cow. Eckles and Roscoe Shaw studied in detail the effect 

 of breed on the percentage of the main constituents. The food 

 ration was kept constant, and samples were taken over practically 

 the whole period of lactation. The same series of investigations 

 was also available to show the variations in composition due to the 

 stage of lactation and to the individual cow. These latter results 

 will be considered later. 



Samples of the daily milk were preserved with formalin, and 

 the estimations carried out once a week. It is impossible here 

 to attempt to reproduce more than a few of the figures obtained 

 by these investigators. The following table gives a summary 

 of the variations in the composition of milk in Jerseys, Holsteins, 

 and Shorthorns, there being three cows in each series : 



Very considerable variations occur, more especially in the fat 

 samples, even when the average estimations are in four-weekly 

 periods. In the Holsteins the fat content was below 3 per cent, 

 and above 5 per cent, in the Jerseys in several averages. 



