11 "2 PerecntfUfe Composttioit of Milk 



teiulod to uive ;i slijilit iucrease in tlic percentage of that constituent in 

 the milk, the deviation from the normal was comparatively slight. 



The work done since V'oit's time has produced rather contradictory 

 results. For example, Ingle (2) found that a protein rich diet increased 

 both the yield of milk and the percentage of fat, while Crowther(3) 

 found that a food rich in protein gave a decrease in the yield but an 

 inc-rease in the fat content. Again, Jordan and Jenter(4) show that the 

 amount of fat in the food is without influence on the percentage of fat 

 in cows" milk, while Morgan, Berger and FingerUng("i) found that a fat 

 poor diet produced in goats a milk with a low percentage of fat. 



There is difficulty in correlating contradictory results such as these, 

 and the difficulty is increased where there is uncertainty as to the calorific 

 value of the food digested and absorbed, and, further, when no account 

 has been taken of the probable influence on the percentage composition 

 of a change in the daily volume of milk secreted. In the voluminous 

 literature on milk there is very Uttle reference to the influence of volume 

 on composition — except in the case of the fat — and it is possible that this 

 may explain some of the contradictory results obtained by different 

 workers on the question of the influence of ditt'erent diets, 



PRESENT IXVESTIGATIOX. 



The present investigation was undertaken to determine : 



A. To what extent variations in the daily volume (or rate of secre- 

 tion) of the milk were accompanied by variations in its percentage 

 composition. 



B. To what extent the percentage composition of the milk could be 

 influenced by diet. 



The experimental animal was the goat, and throughout the investiga- 

 tion the milking was done at 9 a.m. and 5 p.m. The total volume of the 

 24 hours' secretion of milk was measured, mixed and anal)'sed daily, the 

 percentages of total protein, casein, albumin plus globulin, non-protein 

 nitrogen, fat, lactose and ash being determined. 



METHODS OF ANALYSIS. 



Total Protein. The total nitrogen was estimated by the Kjeldahl 

 method, the protein factor G-38 being used for the determination of total 

 protein. 



Casein. The casein was precipitated with acetic acid and filtered off, 

 after which tlie nitrogen was determined by the Kjeldahl method, the 

 same protein factor. (!-38, being made use of. 



