NATURE OF CHYMIFICATION PEPSIN. 507 



bination with many acids, forming compounds which still redden litmus paper ; and it is 

 when thus united with acetic and muriatic acids, that its solvent powers are the greatest. 



6. "In regard to the solvent power of pepsin for coagulated albumen, it was observed by 

 M. Wasmaim that a liquid which contains 17-lO,OOOths of acetate of pepsia, and 6 drops 

 of hydrochloric acid per ounce, possesses a very sensible solvent power, so that it will dis- 

 solve a thin slice of coagulated albumen in the course of 6 or 8 hours' digestion. Witli 12 

 drops of hydrochloric acid per ounce, the white of egg is dissolved in 2 hours. A liquid 

 which contains ^ gr. of acetate of pepsin, and to which hydrochloric acid and white of egg 

 are alternately added, so long as the latter dissolves, is capable of faking up 210 grains of 

 cumulated white of egg at a temper^ure between 95 and 104. It would appear, from 

 such experiments, that the hydrochloric acid is the true solvent, and that the action of the 

 pepsin is limited to that of disposing the white of egg to dissolve in hydrochloric acid. The 

 acid when alone dissolves white of egg by ebullition, just as it does under the influence of 

 pepsin; from which it follows that pepsin replaces the effect of a high temperature, which 

 is not possible in the stomach. The same acid with pepsin dissolved blood, fibrine, meat 

 and cheese; while the isolated acid dissolved only an insignificant quantity at the same 

 temperature; but when raised to the boiling point, it dissolved nearly as much, and the part 

 dissolved appeared to be of the same nature. The epidermis, horn, the elastic tissue (sue!) 

 as the fibrous membrane of arteries), do not dissolve in a dilute acid containing pepsin. M . 

 Wasmann has remarked that the pepsin of the stomach of the pig is entirely destitute of the 

 power to coagulate milk, although the pepsin of the stomach of the calf possesses it in a very 

 high degree ; from which he is led to suppose, that the power of the latter depends upon a 

 particular modification of pepsin, or perhaps upon another substance accompanying it, which 

 ceases to be formed when the young animal is no longer nourished by the milk of its mother."* 



669. It is considered by Liebig, however, that Pepsin has no proper ex- 

 istence as such ; and that it is nothing else than a proteine-compound in a 

 state of change, being, when obtained after the method of Wasmann, the 

 result of the partial decomposition of the membrane of the stomach, which 

 has been induced in it by exposure to air. This view accords well with the 

 fact, recently ascertained by MM. Bernard and Barreswill, that the Saliva and 

 Pancreatic fluid have an equal solvent power when acidulated. In their alka- 

 line condition, their action appears limited to starchy matters ; of which they 

 effect the conversion into sugar. In their acid state, they act, like the gastric 

 fluid, upon azotized matters; and, in common with it, they are destitute 'of 

 power to act upon starch. We are further led, by this remarkable fact (the 

 knowledge of which enables us to harmonize many previous results, which 

 were apparently discordant), to a better understanding of the nature of the 

 action of this Organic compound in the Digestive process. Its operation on 

 starch is precisely that of the substance termed Diastase, which is found in 

 Plants, and which is the agent employed for the conversion of starch into 

 sugar, in various processes of the Vegetable economy. In so doing, it acts as 

 a sort of ferment ; having the power of exciting a change in another substance, 

 in which it does not itself participate. This appears to be precisely the 

 nature of its operation upon azotized matters ; in which it produces an in- 

 cipient change, that so alters their condition, as to dispose them to solution in 

 hydrochloric and acetic acids, with which they form definite chemical com- 

 pounds. The analogy of the action of Pepsin to that of a ferment, is further 

 shown in the power possessed by a very small quantity of it, to excite the 

 required change in an almost unlimited amount of alimentary matters; whilst 

 only a definite quantity of these matters, when thus prepared, can be dissolved 

 in a limited amount of dilute acid; which is precisely analogous to the pro- 

 cess of chemical solution. The agency of Pepsin, in preparing them for that 

 process, resembles that of Heat ; by which it may be replaced, the dilute 

 acids alone, at a high temperature, having the power of dissolving -azotized 

 compounds. 



670. We have, in the last place, to consider the changes which are effected 



* Graham's Elements of Chemistry, [Am. ed. p. C95.] 



