318 THE MECHANICAL FUNCTIONS. 



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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 by 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 not 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 thii5 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. 



\ M. Odler 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. 



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