72 CHEMICAL CONSTITUENTS OF BOD Y AND FOOD. 



pepsin or trypsin. 1 Horbaczewski named the two products of digestion he 

 obtained, hemielastin and elastin-peptone. Chittendeii and Hart, using 

 Kiihne's methods and nomenclature, have shown that hemielastin is 

 protoelastose, and elastin-peptone is deuteroelastose. 



On more complete decomposition elastin yields products very like those 

 obtained from proteids, except that glycocine is obtained, but no aspartic 

 or glutamic acid, and very little tyrosine. 2 Lysatinine but no lysine was 

 obtained. 3 By fusing with potash, indol, skatol, phenol, benzene, but no 

 methylmercaptan, were yielded (Schwartz). 



Reticidin. The fibres of reticular tissue, though histologically not 

 distinguishable from those of areolar tissue, were first stated to be 

 chemically different from them by Mall. 4 He asserted that no gelatin 

 was obtainable from them, a statement corrected by R. A. Young, 5 

 and subsequently by Siegfried. 6 Siegfried, however, confirmed Mail's 

 idea that the fibres contained something special, and separated from 

 them a material he called reticulin. Eeticulin has the following per- 

 centage composition :C, 52-88 ; H, 6*97 ; N, 15-63; S, 1-88; P, 0'34; 

 ash, 2*27. By decomposition it yields sulphuretted hydrogen, ammonia, 

 lysine, lysatinine, and amidovaleriaiiic acid, but no tyrosine and no glu- 

 taminic acid. It gives the proteid reactions with the exception of Millon's. 



Siegfried prepared reticulin from the mucous membrane of the 

 intestine by digestion with trypsin and alkali. The residue was washed 

 and extracted with ether, again subjected to tryptic digestion, and 

 extracted with alcohol and ether ; the collagen was removed by hot water. 



If glutaminic acid is absent, as Siegfried states, from the decomposi- 

 tion products of reticulin, and it is certainly very abundant in the 

 decomposition products of collagen and gelatin, there is distinct evidence 

 that reticulin is a new material. 



We are therefore confronted with the difficulty, that the fibres of 

 reticular tissue are anatomically continuous with and histologically 

 identical with the white fibres of connective tissue, and yet they con- 

 tain chemically this new material. The answer to the problem is pro- 

 bably that reticulin is not specially characteristic of reticular fibres, 

 but is present in all white connective tissue fibres. 



Keratin. Keratin is the horny material of which the horny layer of 

 the epidermis, hair, wool, nails, hoofs, horns, feathers, etc., are composed. 



It is prepared by successively boiling the tissue with ether, alcohol, 

 water, and dilute acid ; the insoluble residue is keratin. A variety of 

 keratin called neurokeratin is found in neuroglia, and has also been 

 described in the medullary sheath of nerve fibres ; though here no doubt 

 some of the histological appearances described maybe artificially pro- 

 duced by reagents. It resembles keratin in its general properties, but 

 is less easily soluble in boiling solutions of caustic potash. 7 



1 Ktihne and Ewald, "Die Verdauung als histol. Metbode," Verliandl. d. naturh.-med. 

 Ver. zu Heidelberg, 1877, N. F., Bd. i. S. 451; Etzinger, Ztschr. f. Biol., Miinchen, Bd. x. 

 S. 84 ; Horbaczewski, loc. cit. ; Morochewetz, Jahr&sb. il. d. Fortsclir. d. Thier-Chem., Wies- 

 baden, 1886, S. 271 ; Chittenden and Hart, loc. cit. 



2 Drechsel, Ladenburg's " Handworterbuch, " Bd. hi.; see also Horbaczewski, Monatsh. 

 d. Chem., Wien, Bd. vi. 



3 See, however, Hediri's recent work referred to on p. 33 of tbis article. 



4 Anat. Anz., Jena, 1888, Bd. iii. No. 14; Abhandl. d. math.-phys. Cl. d. k. sacks. 

 Gesellsch. d. Wissensch., 1887, Bd. xiv. No. 3 ; xvii. No. 14. 



5 Journ. Physiol., Cambridge and London, vol. xiii. p. 332. 



6 " Habilitationschrift," Leipzig, 1892. 



7 Ewald and Kiihne, Verliandl. d. naturh.-med. Ver. zn Heidelberg, N. F., Bd. i. 

 Heft 5 ; Kiihne and Chittenden, Ztschr. f. Eiol., Miinchen, Bd. xxvi. S. 291. 



