300 CHITIN. [BOOK r. 



Arthropoda. Membrane of ovum. Cuticle with its appendages 

 external and internal (setae, apodemata, large tracts of alimentary 

 canal, gizzard when present, all excretory ducts, tracheae of Onycho- 

 phora, Arachnida, Myriapoda and Insecta). 



Chitin is frequently found impregnated with calcareous matter, as 

 in Crustacea, or with silica, as in the radula of the higher Mollusca. 



Pre aration w i n g~ cases f the cockchafer are boiled in 



dilute solution of caustic soda until they have become 

 colourless; they are then washed with water, dilute acids, and 

 lastly with boiling alcohol and ether (Hoppe-Seyler). 



From the shell of the crab or lobster it is obtained by the same 

 treatment, after previous digestion in hydrochloric acid, so as to 

 dissolve the earthy matters deposited in the chitinous tissue. The 

 chitin thus prepared may be dissolved in cold pure concentrated 

 hydrochloric acid, and the solution precipitated by the addition of 

 a large excess of water. 



Pro erties Chitin is a colourless, amorphous body, which retains, 



when prepared by the first of the above-mentioned 

 methods, the form of the parts composed of it ; when prepared by the 

 second method it appears as an amorphous gelatinous body. It is 

 insoluble in water, alcohol, ether, acetic acid, in dilute mineral acids, 

 and in solutions of the alkalies. It is dissolved by concentrated 

 mineral acids. Chitin resists in a very remarkable manner the action 

 'of^alkalies, and can be boiled in their concentrated solutions for long 

 periods of time without undergoing decomposition. 



Elementary Chitin has been subjected to analysis by many 



composition observers. The following is the mean of twelve analyses 

 and formula. ma( je by Ledderhose 1 , who has investigated the con- 

 stitution of chitin under the direction of Professor Hoppe-Seyler. 



Carbon in 100 parts 45'69 



Hydrogen 6'42 



Nitrogen 7'00 



Oxygen 40'89 



Ledderhose * ascribes to Chitin the formula C 15 H 26 N a 10 . 



Berthelot pointed out 2 that when chitin is dissolved 



Products of - in concen trated sulphuric acid it yields a fermentable 



won" 1 ' sugar; this statement has been disproved. The re- 



searches of Ledderhose carried out under the direction 



of Professors Hoppe-Seyler and Baumann have thrown great light 



1 Ledderhose, "Ueber Chitin und seine Spaltungsprodukte." Zeitschrift fur 

 physiol. Chem. Vol. n. (1878), p. 213. Ledderhose: "Ueber Glykosamin. " Ibid. 

 Vol. iv. (1880), p. 139. 



a Berthelot, Comptcs Rendus, XLVII. 227t 



