48 ALIMENTATION. 



great nutritive nitrogenized principle of the blood, and is 

 the substance into which all the principles of this class which 

 exist in food are converted before they are applied to the nu- 

 trition of the tissues. 



Caseine. At a certain period of life this constitutes es- 

 sentially the sole nitrogenized article of food. It is found only 

 in milk, and it exists largely in the great variety of cheeses 

 which are manufactured from milk. In addition to caseine, 

 milk contains butter, sugar, and a variety of inorganic prin- 

 ciples ; and is capable of supplying material for the nourish- 

 ment of all parts of the organism, caseine supplying the nitro- 

 genized principle. In the form of cheese, caseine constitutes 

 an important article of food. 



Fibrin. Fibrin is by no means so important an article 

 of diet as those just considered, and it very seldom forms any 

 considerable part of our food. The same may be said of 

 some other principles of this class, such as globuline, which 

 is the organic principle of the blood-corpuscles; vitelline, a 

 principle peculiar to the yolk of the egg ; osteine and car- 

 tilagine. The two latter substances are generally taken after 

 they have undergone peculiar modifications in cooking, when 

 they are known by other names. 



Gelatine and Chondrine. After prolonged boiling, the 

 organic principles of the bones, integuments, areolar tissue, 

 tendons, and other structures composed of the white fibrous 

 tissue, are dissolved and transformed into a new substance, 

 which is called gelatine. Cartilage, treated in the same 

 way, is in great part converted into chondrine. These two 

 substances are artificial products, and therefore were not 

 considered in treating of the proximate principles of the 



anism. 1 



The principles thus formed are soluble in hot water, 



1 See vol. i., Introduction. 



