74 CHEMICAL CONSTITUENTS OF BODY AND FOOD. 



Amyloid Substance. This material, also called lardacein, occurs in 

 disease in the form of degeneration, called waxy, albuminoid, amyloid, or 

 lardaceous. It principally affects small blood vessels, but it may involve 

 the tissue elements of organs. The degeneration occurs specially in 

 cases of chronic pus formation, and is frequently a sequela of syphilis. 

 The name amyloid was given to it, because the substance is coloured 

 brownish red by iodine, and was supposed by Virchow to be of 

 carbohydrate nature. Friedrich and Kekule 1 were the first to show 

 that it is nitrogenous, and gave as its percentage composition, 0, 53*6 ; 

 H, 7 ; N, 15 ; O, 244. It also contains 1*3 per cent, of sulphur. 2 

 On decomposition it yields leucine, tyrosine, and the other products 

 usually obtained from albuminous matter, but no sugar or other 

 reducing substance. By boiling with alkali a chitin-like residue is left. 3 

 It is slowly soluble in gastric juice. 4 



Skeletins. This term is applied by Krukenberg 6 to a number of 

 nitrogenous substances found in the skeletal tissues of invertebrates. 

 They are characterised by great insolubility, and are probably all 

 amido-derivatives of carbohydrates. Under the term are included 

 chitin, conchiolin, spongin, cornein, fibroin, and sericin. 



Chitin. This substance forms the chief constituent of the ectodermal 

 skeletal tissues of invertebrate animals, especially of arthropods. 6 In 

 Crustacea it is often impregnated with calcareous matter, and in the 

 odontophore of molluscs with silica. According to Krawkow, 7 it is in 

 union with a proteid-like substance. Gibson, 8 Winterstein, 9 and 

 Escombe 10 have found chitin instead of cellulose in several fungi. 



It is prepared from the wing-cases of beetles by boiling them with 

 caustic soda. The chitin remains insoluble ; it may be dissolved in cold 

 concentrated hydrochloric acid, and precipitated unchanged from this 

 solution by the addition of water. It is colourless, amorphous, insoluble 

 in water, alcohol, ether, acetic acid, dilute mineral acids, and concen- 

 trated solutions of the alkalis. It is soluble in concentrated mineral acids. 



The formula and constitution of chitin are differently given by 

 different observers. Ledderhose n gave it the formula C 1;V H 26 N 2 10 . 

 Berthelot 12 stated that it yields a fermentable sugar on boiling with 

 sulphuric acid. Sundwik 13 gave it the formula C (i0 H 100 N 8 38 + ?iH 2 

 (n varying from 1 to 4), and considered it to be an amine derivative of 

 a carbohydrate with the formula (C 12 H 20 10 ) n . Krawkow 14 considers 



I Virchow's Archiv, Bd. xvi. S. 58. 2 Kithne and Rudneff, ibid., BJ. xxxiii. 



3 Krawkow, Centralbl. f. d. med. Wissensch., Berlin, 1892. The resemblance to chitin is 

 supported only by its behaviour to staining agents like iodine. There is no true chemical 

 resemblance between the two substances. Amyloid substance, for. instance, yields no gluco- 

 samine (Colin, Ztschr. f. pliysiol. Chem.. Strassburg, 1896, Bd. xxii. S. 153). 



4 Kostiurin, Wien. med. Jahrb., 1886, S. 181. See also Tschermak, Ztschr. f. pliysiol. 

 Chem., Strassburg, 1895 ? Bd. xx. S. 343. 



6 Ztschr. f. Biol., Miinchen, Bd. xxii. S. 241; " Grundziige einer vergl. Physiol. d. 

 thier. Gertistsubstanz," Heidelberg, 1885. 



6 Gamgee ("Physiol. Chem.." vol. i. p. 299) gives a list of the situations where chitin 

 has been described or inferred to exist. To these must be added the pen of cuttle-fishes 

 (Krukenberg, Ber. d. deutsch. chem. Gesellsch., Berlin, Bd. xviii. S. 989) ; and the cartilages 

 and other mesoblastic structures of the sepia and king crab (Halliburton, Proe. Roy. Soc. 

 London, vol. xxxviii. p. 75). 



7 Ztschr. f. Biol., Miinchen, Bd. xxix. 8 Compt. rend. Acad. d. sc., Paris, tome oxx. 

 9 Ber. d. deutsch. chem. Gesellsch., Berlin, 1894 and 1895. 



10 Ztschr. f. physiol. Chem., Strassburg, 1896, Bd. xxii. S. 288. 



II Ibid., Bd. ii. S. 213 ; iv. S. 139. 



12 Compt. rend. Acad. d. sc., Paris, tome xlvii. p. 227. 



13 Ztschr. f. physiol. Chem., Strassburg, Bd. v. 14 Loc. cit. 



