43 DIGESTION AND FOOD. 



ckondrin, it is found in cartilage and a few other structures. 

 Gelatine is not coagulable like the albuminoid principles, but 

 it is in the form of a tremulous mass when cole}, and liquifies 

 on the addition of heat. It is precipitated by tannic acid, 

 alcohol, aether, and corrosive sublimate, but not by the prus- 

 siate of potash. Its formula is C 82 N 13 H 67 32 . Gregory 

 says that the property of gelatinizing depends on the presence 

 of phosphates; for when gelatine is long boiled with water 

 alone, or with a little alkali, phosphate of lime is deposited, 

 and the solution no longer forms a jelly on cooling. Chond- 

 rine, though regarded as a form of gelatine, differs from it 

 in being precipitated when in solution by acids, alum, and 

 salts of lead, which do not precipitate the latter. 



Gelatine has been considered by various authorities as in- 

 nutritious, but though, like other materials, insufficient in 

 itself to support life, nevertheless it forms one of the useful 

 elements of food. As Lewes says, " Bernard has shown that 

 part of the gelatine is converted into sugar; and sugar, we 

 know, is necessary to the organism. It may also be converted 

 into fat; and, as has been said, there is much evidence to 

 show that it may be converted into albumen, among the com- 

 plex processes of vital chemistry; but whatever may be the de- 

 cision respecting this point, there can be no legitimate reason 

 for denying that gelatine ranks among nutritive principles." 



The conclusions to be drawn from the knowledge possessed 

 regarding the proximate principles of food are : 



Firstly, That they approach as nearly as possible the con- 

 dition in which they exist in animals. 



Secondly, That the want in food of any of the proximate 

 principles of animal tissue often induces a special craving for 

 it, and must be supplied to prevent disorder. 



Thirdly, That no single element contains that which is 

 necessary for the maintenance of life, and we cannot declare 



