194 ELEMENTARY AGRICULTURAL CHEMISTRY 



A considerable difference in the behaviour of the casein of 

 the milks of different animals when treated with rennet (the 

 coagulating enzyme present in the stomach, especially of young 

 animals) is observable. With cows' milk rennet gives a 

 coherent, curdy precipitate ; with human milk or asses' milk 

 the precipitate is much more finely divided, and of course 

 smaller in quantity. This fact has an important bearing upon 

 the feeding of infants, who for this reason often have great 

 difficulty in properly digesting cows' milk. It will also be 

 observed from the figures given in the table that cows' milk 

 differs from the natural food of the human infant in containing 

 much more ash and albuminoids and much less milk sugar. 



Preservation of Milk. — Fresh milk is an important 

 article of diet, and it is a matter of great interest to be 

 able to supply it in a cleanly and uncontaminated state to 

 the consumer. This is rendered the more difficult by the 

 fact that milk serves as an excellent medium for the growth 

 of micro-organisms, which by their life-processes effect pecu- 

 liar chemical changes in several of the constituents. Milk 

 Bugar is particularly liable to undergo decomposition, being 



