INFLUENCE OF FOOD ON ITS COMPOSITION. 343 



been given, the milk exhibits an acid reaction, and has a specific 

 gravity varying from 1-033 to 1-036. It then contains from 2/-46 

 to 22-48-J- of solid constituents, of which from 8 to 11$ are casein, 

 and from 6'84 to 10*95 jj- butter, besides a small quantity of sugar of 

 milk. On mixed food bitches' milk contains more butter and also 

 more sugar of milk. It is a singular circumstance, that on evapo- 

 rating this milk, its sugar is found to be converted into grape- 

 sugar (glucose), and the solid residue attracts a large quantity of 

 oxygen from the air (Bensch). The ash sometimes contains 

 upwards of 93$ of insoluble salts. 



Although there can be no doubt that the 'nature of the food 

 exerts an influence on the composition of the milk, it has not 

 been shown in what manner this affects the individual con- 

 stituents. From the experiments made on bitches, it would 

 appear that a vegetable diet renders the milk richer in butter and 

 sugar; while the solid constituents are augmented when a suffi- 

 cient quantity of mixed food is given. Peligot found the milk 

 of an ass most rich in casein when the animal had been fed on 

 beet-root, whilst it was richest in butter when the food had con- 

 sisted of oats and lucerne. Fat food increases the quantity of the 

 butter. Boussingault found the milk of a cow richer in casein 

 when the animal had been fed on potatoes, than when other food 

 was taken. Reiset found that the milk of cows which were at 

 grass was much richer in fat than when the animals had stood all 

 night in their stalls without food, but Playfair found on the con- 

 trary that the quantity of butter in the milk increased during the 

 night as much as during their stall-feeding, but that the 

 quantity of butter in the milk was considerably diminished by 

 the motion of the animals in the fields an observation which 

 agrees more closely than Reiset's with every-day experience. 

 Hay that has been cut and collected in a dry summer, yields 

 a milk which is richer in butter than hay which has been cut in 

 a wet season. 



It follows from the experiments made by Simon on the milk of 

 a woman who was suckling, that this fluid undergoes gradual 

 alterations during the period of lactation. For while the quantity 

 of the butter remains nearly the same, the casein increases as the 

 child becomes more fully developed, at the same time that the 

 sugar of milk gradually diminishes. The insoluble salts are 

 increased simultaneously with the casein. 



The alterations experienced by the milk from deleterious sub- 

 stances, mental and physical affections, and diseases, have been 



