882 APPENDIX. 



precipitates with this body. Its presence prevents the action of Trommer's sugar- 

 test, since it readily dissolves the precipitated cuprous oxide. The prpteid reactions 

 of glutiri are so feeble that they are probably due merely to impurities. Heated 

 with sulphuric acid it yields ammonia, leucin, and. glycin, but no tyrosin. 



[When gelatin is digested it undergoes alterations similar to those of fibrin and 

 albumin, forming gelatoses and gelatin- peptones, but the results of recent investi- 

 gation indicate that while gelatin is valuable as a food-stuff for furnishing energy, 

 it is not of value for the growth of the nitrogenous tissues. 



It appears improbable^that glutin exists ready-formed in connective-tissue fibres, 

 since these do not swell up in water, and only yield glutin after prolonged treat- 

 ment with boiling water ; to which it may be added that while glutin is acted upon 

 by trypsin, the connective-tissue fibres in their natural condition resist its action 

 (see p. 284). When glutin is submitted for some time to the action of dilute hydro- 

 chloric acid at 38 C., and the change is brought about even more readily by the 

 action of pepsin, it loses its power of gelatinizing and is now diffusible through 

 porous membranes : the name of gelatin-peptone has been given to the product 

 thus obtained. 1 



Elastin. (0, 20.5. H, 7.4. N, 16.7. C, 55.5 percent.) 



This characteristic component of elastic fibres is left on the removal of all the 

 glutin, mucin, etc., from such tissues as "ligamentum nuchae," advantage being 

 taken of its not being altered when it is heated with water, even under pressure, 

 with strong acetic acid, or with dilute alkalies. When moist it is yellow and elastic, 

 but on drying becomes brittle. It is soluble in strong alkalies at boiling tempera- 

 tures, and concentrated sulphuric and nitric acids dissolve it even in the cold ; it is 

 also dissolved by the action of papaya juice. It is precipitated from solutions by 

 tannic acid, but not by the addition of ordinary acids. Notwithstanding that it 

 closely approaches the proteids in its percentage composition, and gives distinct 

 although feeble proteid reactions, any very close relationship between the two ap- 

 pears improbable, since elastin when treated with sulphuric acid, yields leucin ( 30-40 

 per cent, ) only and no tyrosin. 



Hilger 2 has obtained a similar body from the shell membrane of snakes' eggs. 



Keratin. 3 (0, 20.7-25.0. H, 6.4-7.0. N, 16.2-17.7. C, 50.3-52.5. S, 

 0.7-5.0 percent.) 



This body, though somewhat resembling the proteids in general composition, 

 differs from them and also from the preceding bodies so widely in other properties, 

 that its description is placed here for convenience rather than anything else. Hair, 

 nails, feathers, horn, and epidermic scales consist for the most part of keratin. 

 Heated with water in a digester at 150 C. keratin is partially dissolved with evo- 

 lution of sulphuretted hydrogen ; the solution then gives with acetic acid and fer- 

 rocyanide of potassium a precipitate soluble in excess of the acid. Prolonged boiling 

 with alkalies and acids, even acetic, dissolves keratin ; the alkaline solutions evolve 

 sulphuretted hydrogen on treatment with acids. The sulphur in keratin is evi- 

 dently very loosely united to the substance, and in all its reactions there appears to 

 be a want of similarity between keratin and either proteids, mucin or gelatin. The 

 most common of its products of decomposition are leucin (10 per cent.) and tyrosin 

 (3.6 percent), and some aspartic acid; no glycin is formed. What is generally 

 known as keratin is probably a compound body, which has not yet been resolved 

 into its components. 



Ewald and Kuhne 4 have described a new body to which, since it occurs as a constituent of 

 nervous tissue (both of nerves and of the central nervous system), and is yet closely identical with 

 ordinary horny tissue, they give the name of neuro-keratin. It is prepared in quantity from the 

 brain by extracting this tissue with alcohol and ether, and subjecting the residue to the action of 

 pepsin and trypsin. The final residue is neuro-keratin, and amounts to 15 to 20 per cent, of the 

 original tissue. 



Nuclein. C 29 H 49 N 9 P 3 22 . 



Discovered by Miescher 5 in the nuclei of pus corpuscles and in the yellow cor- 

 puscles of yolk of egg. Other observers have subsequently obtained it from yeast, 



1 Hofmeister, Zeitschr. f. physiol. Chem., Bd. ii. (1878), S. 299. 



2 Ber. d. Deutsch. Chem. Gesellsch., 1873, S. 166. But see also next reference. 



8 Linclwall, " Nagra bidrag till kann. om. Ker., Upsala Lakarefs. forh. xvi. (1881), p. 546. 

 * Verhand. Naturhist.-med. Ver., Heidelberg. Bd. i. (1876), Heft 5. 

 5 Med.-chem. Untersuch., Hoppe-Seyler, Heft 4, 1872, S. 441 u. 502. 



