254 COLLAGEN A^ T D GELATTX. [BOOK I. 



Gelatin is insoluble in alcohol, ether and chloroform. It is dis- 

 solved with the aid of heat in glycerin, and on cooling a jelly (glycerin 

 jelly) is obtained. 



Aqueous solutions of gelatin are powerfully laevo-rotatory, the 

 rotatory power being very much influenced by temperature and by 

 the reaction of the solution (Hoppe-Sevler). In aqueous solutions 

 at 30 (a) j = -130. 



Gelatin is not precipitated from its solutions by acetic acid and 

 ferrocyanide of potassium a character which distinguishes it from 

 any proteid substance. It is not precipitated by acetic acid a 

 character which distinguishes it from the closely allied body Chondrin. 



Tannic acid precipitates gelatin even when its solutions are very 

 dilute. Solutions of mercuric chloride also precipitate it. 



On the other hand gelatin is not precipitated by solutions of lead 

 acetate (which precipitates chondrin) nor by the majority of metallic 

 salts which do precipitate the proteids. 



Composi- ^ke u ^imate analyses made of collagen and of 



tion of Geia- gelatin drew the attention of observers to the fact that 

 tin, and its the composition of these two bodies is very similar if 

 relation to no identical. They contain carbon, hydrogen, oxygen, 

 Collagen. nitrogen, and, according to some authors, sulphur. 



The following analyses indicate the composition of these bodies. 



Substance of Gelatin from 

 tendons. tendons. 



Carbon 50"9 50'2 



Hydrogen 7 '2 67 



Nitrogen 18-3 17'9 



O and S 23-5 25'0 



According to Schiitzenberger and Bourgeois, sulphur is not an 

 essential constituent ; these authors ascribe to gelatin the formula 



%HJ?Q*; 



The relations of gelatin to collagen have been made the subject 



of a very interesting study by Hofmeister. This author has found 

 that by heating gelatin for Some time at 130, it loses about 

 0755 per cent, of water and becomes converted into a body in all 

 respects identical with collagen. Collagen is, therefore, probably an 

 anhydride of gelatin. 



The following are the mean results of the analyses of collagen 

 (Hofmeister). 



Carbon 50-75 



Hydrogen 6 -47 



Nitrogen 17 '86 



Oxygen 24 -92 



To gelatin Hofmeister ascribes the formula C ]02 Hj 51 N 31 39 , and 

 collagen is probably related to it as shewn in the following equation: 

 ^N-O^ - H 2 - C^AA, 



Gelatin Collagen 



