THE ORGANIC CONSTITUENTS OF MILK 43 



Engel (1910) believes that an inverse ratio exists between the 

 amount of milk and the amount of fat. He made estimations 

 of the fat in the milk of a number of wet-nurses whose total out- 

 put of milk was known. Some of the data given bear out EngeFs 

 contention, but any very general deduction upon the relationship 

 of the amount of milk to the fat content is hardly justifiable from 

 his figures. 



Helbich (1911), who carried out careful investigations upon 

 the fat content in relation to the total amount of milk given at 

 each feed, was unable to trace any relationship between the two. 

 The diagram on p. 26 shows the results of one set of observations 

 made by him, and the others are on the same lines. The fat content 

 was usually lowest in the morning, rising considerably at one of 

 the next feeds. In the diagram the 10 A.M. feed gave the highest 

 percentage of fat, but this was not found in all the experiments. 



This is in general harmony with the observation of Eckles 

 and Shaw on the variation in fat content of cows' milk due to 

 different intervals of milking. They state that the milk about 

 midday usually had the highest fat content. 1 



The average fat content of human milk is higher than that 

 of cows' milk, although in the case of the cow variations due to 

 breed, &c., may raise the level to that of human milk. Great 

 individual variations also occur in both cases, as well as differences 

 from other causes dealt with on pp. 22-26. 



A great deal of work has been done on the composition of the 

 fat of both human and cows' milk, but there is no evidence to show 

 that such differences in composition as may occur have any bearing 

 upon the health of either infants or adults, and the subject will 

 not be considered here. 



Reference may be made to the work of Arnold on human fat, 

 where references to the literature upon this point, both for human 

 and cows' milk, are also given. Eckles and Shaw give elaborate 

 data upon the fat of cows' milk, with literature. 



Attempts have been made to produce an increased fat content 

 in the milk by feeding on fat. Engel and Plaut found that 

 increasing the fat in the food, even considerably, did not enable 

 any appreciable increase in the fat content to be detected in the milk 

 of a normally-nourished woman. If the intake of fat is below the 

 amount required for the usual metabolism, the amount of fat in the 

 milk is reduced. 2 These results are in agreement with those obtained 

 in numerous investigations upon other constituents of milk. Similar 

 work relating to the sugar content is given on the next page, and 

 that relating to the inorganic constituents in the next chapter. 



The experiments conducted by Woll on the amount of butter- 

 fat produced by cows in relation to their food are of great interest. 

 Cows fed on a food which is below the minimal physiological require- 



1 Cp. p. 25. z Cp. p. 21. 



