840 THE SKIN AND ITS SECKETIONS. 



ing to v. FURTH and Russo on cleavage it yields 25 per cent acetic acid 

 and 60 per cent glucosamine. The formula is (C28H<5oN40i9)z according 

 to v. FURTH and collaborators and splits according to the equation: 

 (C28H5oN 4 Oi9)4+5zH 2 O = 4s(C 6 Hi3N05)+2z(CH 3 COOH). According 

 to BRACK, who admits of at least four glucosamine groups in chitosan, 

 the formula for chitin is (C32H54N402i)x and contains 4 acetyl for every 

 4 nitrogen atoms. The transformation into chitosan consists in a 

 rupture of one-half of the acetic acid groups in the chitin. 



In a dry state chitin forms a white, brittle mass retaining the form 

 of the original tissue. It is insoluble in boiling water, alcohol, ether, 

 acetic acid, dilute mineral acids, and dilute alkalies. It is soluble in 

 concentrated acids. It is dissolved without decomposing in cold con- 

 centrated hydrochloric acid, but is decomposed by boiling hydrochloric 

 acid. According to KRAWKOW the various chitins behave differently 

 with iodine or with sulphuric acid and iodine, in that some are colored 

 reddish brown, blue, or violet, while others are not colored at all. Accord- 

 ing to WESTER chitin free from chitosan is not colored by iodine. 



Chitin may be easily prepared from the wings of insects or from the shells 

 of the lobster or the crab, the last-mentioned having first been extracted by an 

 acid so as to remove the lime salts. The wings or shells are boiled with caustic 

 alkali until they are white, afterward washed with water, then with dilute acid 

 and water. The pigments remaining can be destroyed by permanganate. The 

 excess of this last can be removed by a dilute solution of bisulphite, washed with 

 water and then extracted with alcohol and ether. 



Hyalin is the chief organic constituent of the walls of hydatid cysts. From a 

 chemical point of view it stands close to chitin, or between it and protein. In 

 old and more transparent sacs it is tolerably free from mineral bodies, but in 

 younger sacs it contains a great quantity (16 per cent) of lime salts (carbonate, 

 phosphate, and sulphate). 



According to LUCRE l its composition is: 



C H N O 



From old cysts 45.3 6.5 5.2 43.0 



From young cysts 44.1 6.7 4.5 44.7 



It differs from keratin on the one hand and from proteins on the other by the 

 absence of sulphur, also by its yielding, when boiled with dilute sulphuric acid, 

 a variety of sugar in large quantities (50 per cent), which is reducing, fermentable, 

 and dextrogyrate. It differs from chitin by the property of being gradually 

 dissolved by caustic potash or soda, or by dilute acids; also by its solubility on 

 heating with water to 150 C. 



The coloring matters of the skin and horn-formations are of different 

 kinds, but have not been extensively studied. Those occurring in the 

 stratum Malpighii of the skin, especially of the negro, and the black 

 or brown pigment occurring in the hair, belong to the group of those 

 substances which have received the name melanins. 



1 Virchow's Arch., 19. 



