SKELETINS. 75 



that there are a number of chitins, amine derivatives of different 

 carbohydrates (dextrose, glycogen, dextrin, etc.) ; they give different 

 colour reactions with iodine. 1 Ledderhose 2 was the first to show that 

 the reducing substance obtained by the action of mineral acids in 

 chitin is not sugar but glucosamine (see p. 9). The equation re- 

 presenting its decomposition he gives as follows : 



2C 15 H 20 N 2 10 + 6H 2 = 4C 6 H 13 NO 5 + 3C 2 H 4 2 



(chitin) (water) (glucosamine) (acetic acid) 



Glucosamine is an amido-derivative of glucose ; it forms crystalline 

 salts, of which the hydrochloride is readily prepared by boiling chitin 

 with hydrochloric acid ; this is soluble in water, and is dextrorotatory 

 () D r=:-f70 -G. The base is prepared by the action of baryta on the 

 sulphate. It is crystalline and not fermentable with yeast. 



Schmiedeberg 3 looks upon chitin as an acetyl derivate of glucosamine, 

 and as he has also obtained the latter substance from the chondroitin- 

 sulphuric acid of cartilage, he regards it as indicating a connection 

 between the skeletal tissues of vertebrate and invertebrate animals. 



By heating chitin with ten times its weight of caustic alkali at 180, 

 Hoppe-Seyler and Araki 4 obtained a substance which possesses the 

 original form of the pieces of chitin, but differs from chitin in being 

 very soluble in dilute acids such as acetic acid ; from such solutions it is 

 precipitable by alkalis. This substance is called chitosan, and its forma- 

 tion from chitin. is shown in the following equation : 



C 18 H3 N 2 12 + 2H 2 O =C U H 26 N 2 10 +2C 2 H 4 2 



(chitin) (water) (chitosan) (acetic acid) 



Chitosan in dilute acetic acid is levorotatory ; () D = - 17'7 to 17*9. 

 By heating it with acetic acid in sealed tubes to 135, a substance 

 very like chitin is regenerated ; it, however, contains three, whereas 

 true chitin only contains two acetyl groups. 



By boiling with concentrated hydrochloric acid, chitosan yields 

 hydrochloride of glucosamine, formic and acetic acids. 



Neurocliitin. In Crustacea, chitin has been said to take the, place of neuro- 

 keratin as a support to the nerve fibres. 5 



Concliiolin (C 30 H 48 N 9 O n ) forms the organic basis of the shells of mussels 

 and snails. On decomposition it yields leucine, perhaps glycociiie, but no 

 tyrosine or reducing substance. It does not give the xanthoproteic, Millon's, 

 nor the Adamkiewicz reactions. The byssus of molluscs is similar. The 

 cementing substance between the eggs of various molluscs contains a substance 

 more like keratin. Cornein, from corals (C 80 H 44 ]Sr 9 33 ), differs from conchiolin 

 by giving a red colour with Millon's test ; on decomposition it yields leucine 

 and a crystalline material called cornicrystallin. 



Spojigin, the organic basis of the common sponge, yields as decomposition 

 products, leucine and glycocine (Stadeler), but no tyrosine. 6 It does not give 

 the colour reactions just mentioned ; it resembles conchiolin by yielding 



1 E. Zander (Arch. f. d. ges. PhysioL, Bonn, 1897, Bd. Ixvi. S. 545) also finds that 

 chitin gives a colour with iodine very like that given by glycogen. 



2 Ztschr.f. physiol. Chem., Strassburg, Bd. ii. S. 213 ; iv. S. 137. 



3 Arch. f. exper. Path. u. PharmakoL, Leipzig, Bd. xxviii. 



4 Bar. d. deutsch. chem. Gesellsch., Berlin, 1894, Bd. xxvii. S. 3329 ; 1895, Bd. xxviii. S. 

 82 ; Zfschr. f. phijsiol. Chem., Strassburg, 1895, Bd. xx. S. 498. 



5 Griffiths, Compt. rend. Acad. d. sc., Paris, tome cxv, 



<; Zalocostas (ibid., tome cvii. p. 252), however, obtained tyrosine, butalanine, and 

 glucalanine (C H 18 N 8 4 ). 



