72 CHEMICAL CONSTITUENTS OF BODY AND FOOD. 
pepsin or trypsin. 1 Horbaczewski named the two products of digestion he 
obtained, hemielastin and elastin-peptone. Chittenden 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.- Lysatinine but no lysine was 
obtained. 3 By fusing with potash, indol, skatol, phenol, benzene, but no 
methylmercaptan, were yielded (Schwartz). 
Reticulin, — 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 Mall's 
idea that the fibres contained something special, and separated from 
them a material he called reticulin. Reticulin has the following per- 
centage composition :— C, 52SS ; H, 6*97; N, 15-63; S, 1-88; P, 034; 
ash, '2-27. By decomposition it yields sulphuretted hydrogen, ammonia, 
lysine, lysatinine, and amidovalerianic acid, but no tyrosine and no glu- 
taminic acid. It gives the proteid reactions with the exception of MUlon'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 glutaininic 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 7 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 may be 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 Kuhne and Ewald, "Die Yerdauung als histol. Methode," Vcrhandl. d. naturh.-med. 
Ver.su Heidelberg, 1877, N. F., Bd. i. S. 451; Etzinger, Ztschr. f. Biol., Miinchen, Bd. x. 
S. 84 ; Horbaczewski, loc. cit. ; Morochewetz, Jahresb. ft. d. Fortschr. d. ITiier-Chem., "Wies- 
baden, 1886, S. 271 ; Chittenden and Hart, loc. cit. 
- Drechsel, Ladenburg's "Handworterbuch," Bd. iii. ; see also Horbaczewski, Afonatsh. 
d. Chem., Wien, Bd. vi. 
3 See, however, Hedin's recent work referred to on p. 33 of this article. 
4 Anat. Anz., Jena, 18S8, Bd. iii. No. 14; Abhandl. d. math. -phys. CI. d. k. sacks. 
Gesellsch. d. JFissensch., 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 Kuhne. Verhandl. d. naturh.-med. Ver. vu Heidelberg, N. F.. Bd. i. 
Heft 5 ; Kiihne and Chittenden, Ztschr. f. Biol., Miinchen, Bd. xxvi. S. 291. 
