CHITIN. 791 



Chitin is not found in vertebrates. In invertebrates chit in is alleged 

 to occur in several classes of animals; but it can be positively asserted 

 that true, typical chitin is found only in cephalopods and in articulated 

 animals especially, in which it forms the chief organic constituent of 

 the shell, etc. KRAWKOW 1 found that chitin of the shell, etc., does 

 not seem to occur free, but in combination with another substance, prob- 

 ably a protein-like body. In GILSON and WINTERSTEIN'S 2 investigations 

 chitin occurred in certain fungi as well. 



According to SUNDVIK the formula of chitin is probably CeoHiooNgOas 

 + n(H2O), where n may vary between 1 and 4. ARAKI claims that it 

 has on the contrary the composition Ci8H 3 oN2Oi2. KRAWKOW found 

 that the chitins of different origin show different action with iodine, 

 and he therefore concludes that there must exist quite a group of 

 chitins, which seem to be amino derivatives of different carbohydrates, 

 such as dextrose, glycogen, dextrins, etc. According to ZANDER 3 only 

 two chitins exist, one of which turns violet with iodine and zinc 

 chloride, and the other brown. 



Chitin is decomposed on boiling with mineral acids and yields, as 

 shown by LEDDERHOSE, glucosamine and acetic acid. HOPPE-SEYLER 

 and ARAKI found on heating with alkali and a little water to 180 that 

 chitin was split into a new substance, chitosan, and acetic acid, and that 

 this chitosan contained acetyl groups as well as glucosamine. Chitin 

 can hardly be considered as a simple acetyl glucosamine, but probably 

 has a much more complicated constitution, which is not known at the 

 present. FRANKEL and KELLY as well as OFFER 4 have obtained acetyl 

 glucosamine, C 6 HiiO 5 NH(COCH 3 ) and acetyldiglucosamine (C^H^^Og) 

 COCH 3 as characteristic cleavage products. 



The acetyldiglucosamine has the same empirical formula, Ci4H 2 6N 2 Oio, 

 as the chitosan prepared by ARAKI, but it is not identical therewith. 

 The chitosan, which v. FURTH and Russo 5 obtained as a crystalline 

 hydrochloric acid combination, has a different composition, and accord- 

 ing to them, is more likely a multiple of C^H^N^O^. On heating 

 with acetic anhydride chitosan is converted into a chitin-like substance 

 which is not identical with chitin. Chitosan is insoluble in water and 

 alkali, but dissolves in dilute acids. It splits into acetic acid and gluco- 

 samine by the action of hydrochloric acid. According to v. FURTH and 



rend., 47; Winterstein, Zeitschr. f. physiol. Chem., 18; Franchimont, Ber. d. deutsch 

 chem. Gesellsch., 12. 



1 Zeitschr. f . Biologic, 29. 



2 Gilson, Compt. rend., 120; Winterstein, Ber. d. deutsch. chem. Gesellsch., 27 and 28. 



3 Sundvik, Zeitschr. f. physiol. Chem., 5; Araki, ibid., 20; Zander, Pfluger's Arch., 66. 



4 Ledderhose, Zeitschr. f. physiol. Chem., 2 and 4; Araki, 1. c.; Frankel and Kelly, 

 Monatshefte f. Chem., 23; Offer, Bioch. Zeitschr., 7. 



5 Hofmeister's Beitrage, 8. 



