726 MUCIX, GELATIN, ETC. [App. 



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 treatment 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. 253). When glutin is 

 submitted for some time to the action of dilute hydrochloric acid, at 

 38 C., and the change is brought about even more readily by the action 

 of pepsin, it loses its power of gelatinising 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, 74. N, 16-7. C, 55-5 p. c.) 



This characteristic component of elastic fibres is left on the removal 

 of all the glutin, mucin, &c. from such tissues as " ligamentum nuchoe," 

 advantage being taken of its not being altered when it is heated with 

 water, even under pressure, with strong acetic acid, or with dilute 

 alkalis. When moist it is yellow and elastic, but on drying becomes 

 brittle. It is soluble in strong alkalis at boiling temperatures, 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 per- 

 centage composition, and gives distinct although feeble proteid reactions, 

 any very close relationship between the two appears improbable, since 

 elastin when treated with sulphuric acid, yields leucin (30 40 p.c.) 

 only and no tyrosin. 



Hilger 2 has obtained a similar body from the shell membrane of 

 snakes' eggs. 



Keratin 3 . (0, 20-725-0. II, G-4-7-0. N, 16-217-7. C, 

 50-352-5. S, -75-0 p.c.) 



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 evolution 

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

 ferrocyanide of potassium a precipitate soluble in excess of the acid. 

 Prolonged boiling with alkalis and acids, even acetic, dissolves keratin ; 

 the alkaline solutions evolve sulphuretted hydrogen on treatment with 



1 Hofmeister, Zeitsch. f. physiol. Chem. Bd. n. (1878), S. 299. 



2 Ber. d. deutsch. chem. Gesellsch. 1873, S. 166. But see also next reference. 



8 Lindwall, "Nagra bidragtiil kann. om. Ker. Upasala Lfikarefs. fork, xvi. (1881), 

 p. 546. 



