318 THE MECHANICAL FUNCTIONS. 



In external appearance their texture approaches 

 nearer to that of horn than to any other animal 

 product : yet in their chemical composition they 

 differ from all the usual forms of albuminous 

 matter. The substance to which they owe their 

 characteristic properties is of a very peculiar 

 nature; it has been termed Chitine^j M. Odier,* 

 and Entomoline by M. Lassaigne.f This sub- 

 stance is found in large quantity in the wings 

 and elytra of coleopterous insects. It is re- 

 markable for riot liquefying, as horn does, by 

 the action of heat ; and accordingly the integu- 

 ments of insects, even after having been sub- 

 jected to a red heat, and reduced to a cinder, 

 are found to retain their original form. \ 



With this substance there is blended a quan- 

 tity of colouring matter, which has usually a dull 

 brown or black hue. But the colour of the ex- 

 ternal surface is generally owing to another por- 

 tion of this matter, which is spread over it like a 

 varnish, and being soluble in alcohol and in 

 ether, may be removed by means of these agents. 

 The colours which are displayed by insects, and 



* Annales de Chimie, torn. 76. 



f See the work of Straus Durckheim, p. 33. 



J M. Odier had concluded from his experiments that no ni- 

 trogen enters into the composition of this substance. That this 

 conclusion has been too hastily adopted has been proved by Mr. 

 Children, who, by pursuing- another mode of analysis, found that 

 the chitine of cantharides contains not less than nine or ten per 

 cent, of nitrogen. See Zoological Journal, i. Ill 115. 



