122 Percentage Comjfosition of Mil h 



representing the protein would be at different angles, as the protein 

 neither rises nor falls with variations in volume to the same extent as 

 the fat, but the likeUhood is that where Tocher uses the word "quality" 

 the words "percentage of protein" might be substituted, without im- 

 pairing the accuracy and applicability of the statement. 



During the present investigation the individual protein constituents 

 were estimated as casein on the one hand, and albumin plus glol)ulin 

 on the other, and it was found that, from day to day, the casein and 

 albumin plus globulin were present in varying proportions. Sometimes, 

 when there was a rise in the percentage of protein, it was found that this 

 was due chiefly to the casein; and again, on some other occasion, the 

 albumin and globulin would be found to have contributed largely to the 

 rise. Despite these irregularities, however, it was found that there was 

 a tendency for the casein on the one hand, and the albumin plus globulin 

 on the other, to maintain individually, as well as in combination, an 

 inverise percentage relationship to volume ; and, consequently, these 

 protein constituents of the milk were found present in larger percentages 

 at the beginning and end of lactation than during the period when it 

 was at its height. 



With regard to the ash, this was found to he the least variable of the 

 constituents of the milk, but the analytical data for E.xps. II and V 

 show that where there was a marked fluctuation in volume the percentage 

 of a.sh .showed an inverse relationship to it. 



The relationship of lactose to volume is not so apparent as that of 

 the protein or fat. Crowther and Euston(S) say: "It will be seen that 

 the percentage of sugar, after rising a httle with the early stages of lacta- 

 tion, fell steadily throughout the rest of the period." While due credit 

 must be given for this observation it nuiy be pointed out that the per- 

 centage of lactose is only indirectly connected with the period of lacta- 

 tion. Its real relationship is to volume, and the accuracy of the words 

 "steadily throughout" would seem to depend on the evenness with 

 which the volume rises at the commencement of lactation, the evenness 

 with wliich it is maintained, and the evenness with which it falls at the 

 end of lactation. During the present investigation, where there were 

 wide variations in volume at the height of lactation, due either to dieting 

 or starvation, the percentage of lactose was found to vary also, and 

 showed a direct relationship to it — as may be seen in Fig. 4. 



The inter-relationship of vohime and com])osition suggests a theory 

 of milk secretion which may be put forward here, and on wliich further 

 work is being carried out. 



