CHITIN. 403 



resembles vegetable bodies and especially vegetable fibre, may be 

 regarded as composed of a carbo-hydrate similar to cellulose, and 

 of a nitrogenous body which has the composition of the muscular 

 fibre of insects. The latter is represented, according to his ana- 

 lyses, by the formula C 8 H 6 NO 3 ; and C 17 H 14 NO n -C 8 H 6 NO 3 = 

 C 9 H 8 8 . 



Preparation. The best method of obtaining this body is by 

 boiling the elytra of the cockchafer with water, alcohol, ether, 

 acetic acid, and alkalies ; the body always perfectly retains the 

 structure of the elytrum, or of the other insect-tissues from which 

 it is prepared. 



Physiological Relations. 



This body forms the true skeleton of all insects and Crustacea. 

 It constitutes not merely their external skeleton, the scales, hairs, 

 &c., but also forms their tracheae, and thus penetrates into the 

 minuter portions of the organs ; indeed even one of the layers of 

 the intestinal canal of insects consists of chitin ; hence we can 

 very well prepare all these parts by treating insects with a solution 

 of potash and then microscopically examine the finest parts, as for 

 instance, the valves of the tracheal openings. 



If Schmidt's hypothesis regarding the constitution of chitin be 

 confirmed by further observations, it would be easy to understand 

 how this substance is formed from the food of insects. 



In reference to its application in the insect organism, chitin is 

 at most entitled to be regarded as a histogenetic substance. 



Before concluding our remarks on the organic substrata of the 

 animal organism we would briefly review the mode of arrangement 

 in which these substances have been considered. We observed in 

 our remarks introductory to the subject of Zoo-Chemistry that the 

 physiological and chemical classifications of animal substances 

 must perfectly coincide with one another ; and now in our conclu- 

 ding observations we are constrained to admit that our knowledge 

 of the organic substrata of the animal body is still very deficient, 

 and that we have been provisionally compelled to adopt a practical 

 classification and arrangement, in which, passing from the simpler 



2 D 2 



