MILK. 95 



nutritive matter demanded by the child. Lacto-proteine, 1 a 

 principle described by Millon and Commaille, is not so well 

 defined, and albumen exists in the milk in very small quan- 

 tity. That albumen always exists in milk can readily be 

 shown by the following process described by Bernard : 

 If milk, treated with an excess of sulphate of magnesia so as 

 to form a thin paste, be thrown upon a filter, the caseine 

 and fatty matters will be retained, and the clear liquid 

 that passes through shows a marked opacity upon the ap- 

 plication of heat or the addition of nitric acid. 2 



The coagulation of milk depends upon the reduction of 

 the caseine from a liquid to a semisolid condition. ^Vhen 

 milk is allowed to coagulate spontaneously, or sour, the 

 change is effected by the action of the lactic acid which re- 

 sults from a transformation of a portion of the sugar of milk. 

 Caseine, in fact, is coagulated by any of the acids, even the 

 feeble acids of organic origin. It differs from albumen in 

 this regard, and in the fact that it is not coagulated by heat. 

 It has been suggested that in fresh milk the caseine exists 

 in combination with carbonate of soda, and that coagulation 

 always takes place from the action of acids upon this salt, 

 by which the caseine is set free. It is true that coagulated 

 caseine may be readily dissolved in a solution of carbonate 

 of soda, but it has been shown by the experiments of Selmi, 

 that coagulation may be induced by the agency of certain 

 neutral principles, while the milk retains its alkaline reac- 

 tion. If fresh milk be slightly raised in temperature, and 

 be treated with an infusion of the gastric mucous membrane 

 of the calf, coagulation will take place in from five to ten 

 minutes, the clear liquid still retaining its alkaline reaction. 8 

 This observation has been repeatedly confirmed. Simon 



1 MILLOX ET COMMAILLE, Nouvdle substance albumio'ide contenue dans le lait. 

 Cornptes rcndus, Paris, 1864, tome lix., p. 301. 



2 BERNARD, Liquides de rorganisme, Paris, 1859, tome ii., p. 224. 



3 SELMI, RecJierches sur faction de la prtsure dans la coagulation du lait, 

 Journal de pharmacie et de chimie, Paris, 1846, 3me serie, tome ix., p. 265. 



