MUNICIPAL HYGIENE 707 



There are various causes which influence the composition 

 of the secretion, which in the examination of a single 

 sample would have to be borne in mind. For instance, 

 the first portion of milk drawn from the udder is more 

 watery than the last ; in fact, during the whole process of 

 milking there is a gradual increase in the total solids, more 

 noticeable, however, in the fat constituent than in the solids 

 not fat. 



The morning milk usually contains from J to 1 per cent. 

 more water than the evening milk, or to state the case 

 another way the evening milk is richer than the morning. 

 There is also a difference in the composition depending 

 upon whether the animal is milked twice or three times a 

 day ; in the latter case the fat is higher than in the former. 



The age of the cow is not without influence, the maximum 

 amount of milk produced is generally between the fourth 

 and fifth calf. A large yield of milk may, but not neces- 

 sarily, mean a milk of poor quality. Breed is of the utmost 

 importance in the composition of milk ; in the Jersey, for 

 example, the milk is very rich, in fact, comparing the 

 Jersey with another excellent milking breed, viz., Ayrshire, 

 there may be as much as 2 per cent, more fat and 2 per 

 cent, less water in the milk of the former as compared 

 with the latter. 



The period of lactation is another factor to bear in mind, 

 and here the fat is the main constituent affected. Taking 

 the average period of lactation at about 300 days, it is 

 found that practically there is throughout the whole of this 

 time a gradual increase in the amount of fat secreted. 



Diet also influences the composition of the secretion; 

 one deficient in proteids produces a poorer milk than a diet 

 in which this exists in proper proportion. It is considered 

 by some that the influence of diet is not so marked as the 

 influence of breed ; but the influence of good feeding on the 

 quantity and quality of the milk is extraordinary. Eegu- 

 larity in milking and kind treatment are both factors which 

 influence the composition of the secretions. 



The milk secreted for a few days after calving is, of 

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