Milk and Its Products. 277 



continued feeding of nutrients entirely from the corn plant, as 

 well as from the wheat plant, tended to produce soft, low-melting 

 milk fats, while the nutrients from the oat plant produced fats 

 making a hard butter, with a high melting point. 



Season. The influence of season upon the composition of milk, 

 apart from the effect of advancing lactation, is largely associated 

 with the food supply. When this is normally maintained and 

 the animals are protected from the effect of weather changes, 

 variations in the composition of the milk appear to be slight. 



Time and intervals between milking. Where the time be- 

 tween milkings is the same and there are no other disturbing in- 

 fluences, the composition of morning's and evening's milk shows 

 practically no difference. Where the intervals are unequal, 

 there may be a considerable variation in the two milkings. In 

 an experiment where 17 Shorthorn cows were milked at 6 a. m. 

 and 3 p. m. the average per cent of fat in the morning's milk was 

 3.2, and 4.5 per cent in the evening's milk. 



It is well known that the first milk drawn from the udder at 

 milking time is very low in fat, sometimes being as low as 1 per 

 cent, while the last portion may contain as high as 10 per cent. 

 In these two fractions, however, the other constituents are in 

 about the same proportion as would be found in the entire milk- 

 ing. 



Milk of other animals. The following table compiled from 

 several sources, gives the average composition of the milk of 

 other animals; some of the results are probably not truly rep- 

 resentative, due to improper sampling. 



There is a considerable difference in the behavior of the casein 

 of the milk of different animals when treated with rennet. With 

 cow's milk the enzyme of rennet, rennin, gives a coherent, curdy 

 precipitate, while with human milk the coagulum is much more 

 finely divided. To this fact has been attributed, in part, the 

 non-adaptability of cow's milk to infant feeding. It will also 

 be noticed that cow's milk differs from the natural food of the 

 human infant in containing more ash and proteins and much less 



