CHAP. VII I.] EPITHELIAL TISSUES, &C. 301 



upon the decomposition, and have shewn that when heated with 

 acids chitin combines with the elements of water and splits up into a 

 nitrogenous body glycosamine and into acetic acid, thus : 



2 (C U IW) 10 ) + 6H 2 = 4(C 6 H 13 N0 5 ) + 3(C 2 H 4 2 ). 



''/. 



Glycosamine, 6 H 13 N0 5 . 



Prepara- Chitin is soluble in cold concentrated HC1, and the 



tton. solution remains colourless when exposed to air, the dis- 



solved body not undergoing decomposition and being thrown down 

 unchanged by the addition of water. 



When the solution is boiled it becomes black, in consequence of 

 a decomposition which is completed in about an hour. On evaporation, 

 impure hydrochlorate of glycosamine is obtained, and is purified by re- 

 crystallizing repeatedly. 



The amount of this compound formed amounts to 70 or 75 p.c. of the 

 weight of the chitin dissolved. 



Properties. The hydrochlorate of glycosamine is easily soluble in 

 water, but soluble with difficulty in alcohol ; its solution has a sweet taste and 

 an acid reaction. It reduces alkaline solutions of cupric and silver salts, 

 and its solutions react like solutions of glucose when boiled with caustic 

 alkalies. It is dextro-rotatory (a) D = + 70- 6. The pure base (prepared by 

 the action of barium hydrate on the sulphate of glycosamine) crystallizes 

 from alcohol in the form of needles. It is not fermentable. 



Probable Ledderhose considers glycosamine to be an amido-deriva- 



constitution. tive of grape sugar (dextrose), thus : 



COH . (CHOH) 4 . CH 2 OH COH . (CHOH) 4 CH 2 NH 2 



Dextrose. Glycosamine. 



Conchiolin. 



The organic matter of the shells of Mussels and Snails was 

 formerly supposed to be identical with chitin; this is not, however, 

 the case, and to the substance the name of Conchiolin has been 

 applied. 



Prepara- The shells of mussels are macerated in dilute hydro- 



tion - chloric acid ; then boiled in aqueous solutions of the 



caustic alkalies. 



Elementary The differences in composition between Conchiolin 



composition. and chitin are shewn by the two analyses quoted below: 



Conchiolin. Chitin. 



Carbon .... 507 . . . 46'32 



Hydrogen . . . . 6*5 . . . 6 '40 



Nitrogen . . . . 167 . . . 614 



Oxygen .... 261 . . . 4114 



X 



