84 CHEMICAL COMPOSITION OF THE BODY. 



from its solution by exact neutralization, is easily soluble in dilute acids and 

 alkalies, and in solutions of the alkaline carbonates, but it is quite insoluble 

 in solutions of common salt, and the chlorides of ammonium and calcium. 

 It does not decompose peroxide of hydrogen. The acid solutions of syntoniu 

 do not coagulate at a boiling temperature. 



54. DERIVATIVES OF ALBUMEN. In close relationship with the albu- 

 minous compounds, stand a series of substances into which albumen is either 

 converted in the act of digestion, as peptone, or which may be obtained from 

 various secretions and tissues, as ptyaliu, pepsin, and paucreatin, which 

 constitute the organic bases of the salivary, gastric, and pancreatic fluids, 

 respectively; mucin, contained in mucus; spermatin, from the spermatic 

 fluid ; elastin, keratin, collogen, cerebrin, and choudrin, which are severally 

 found in elastic, horny, and connective tissue, in the nervous tissue, and in 

 cartilage. These are all azotized. Most of them contain sulphur and, like 

 albumen, have a great tendency to imbibe water and swell up. They have 

 but little disposition to undergo putrefaction. 



PTYALIN is obtained by acidulating saliva with phosphoric acid, and pre- 

 cipitating with lime-water. The Ptyalin falls with the phosphate of lime, 

 from whence it may be extracted by distilled water. It contains nitrogen, 

 and is thrown down from its watery solution by alcohol, but its reactions 

 show conclusively that it is not identical with albumen. Great interest is 

 attached to it in consequence of its remarkable power of converting starch 

 into sugar. 



PEPSIN may be obtained from the gastric juice, in a pure or nearly pure 

 state, by a method suggested by v. Wittich, 1 which consists in making an 

 extract of the mucous membrane of the stomach with glycerin, after co- 

 agulating the albuminous compounds with alcohol. Pepsin is a grayish- 

 white, amorphous, nitrogenous substance, which is not hygrometric, and is 

 incapable of assuming the crystalline form. It dissolves with difficulty in 

 water, but more easily in dilute acids, and then possesses powerful digestive 

 properties. It is a colloid, *'. e., is non-diffusible per se, 2 but its acid solution 

 readily diffuses. 3 It is precipitated by platinum chloride, and by the neu- 

 tral and basic acetates of lead, but not by concentrated nitric acid, iodine, 

 tauuic acid, or bichloride of mercury. The pepsin of the shops is very 

 impure, containing, with some pepsin, much peptone and starch ; yet its 

 activity is considerable. Pepsin acts energetically when combined with 

 from 0.1 to 7 per cent, of hydrochloric or sulphuric acid; with 0.2 to 12 

 per cent, of ordinary phosphoric acid ; with 0.1 to 5 per cent, of nitric acid; 

 and with from 1 to 5 per cent, of acetic, lactic, and oxalic acids. In order 

 that its solvent powers should be exerted, it is imperatively necessary that 

 it should possess an acid reaction ; the neutralization of its normal acidity 

 with sodium carbonate having been shown by Bernard to effect the imme- 

 diate arrest of the digestive process. An exceedingly small quantity of 

 pepsin, in the first instance, will suffice to dissolve a very considerable amount 

 of fibrin, providing fresh additions of diluted acid be constantly made; the 

 pepsin appearing to determine the solution of the albuminoid substance in 

 the acid. The temperature most favorable for the performance of artificial 

 digestion is betweeu 95 aud 112 F. A boiling temperature, aud even 

 one not exceeding 140 F., deprives pepsin of its peculiar properties; and 

 scarcely any digestion occurs at a temperature of 40 F. 



GELATIN OR COLLAGEN. This substance is not an original constituent 



1 Pflii-jrr's Archiv, Band v, 1873. 



2 Wuliriiii<r<'], IMluuvr's Archiv, 1873, Hand vii, p. 188. 



3 Sec v. Wittich, Pfliiger's Archiv, 1872, Band v, p. 435. 



