342 OF DIGESTION AND NUTRITIVE ABSORPTION. 



liquor being filtered is found to have the property of reducing most alimentary 

 substances, submitted to its action at a slightly elevated temperature ; even 

 though the membrane have been previously dried. Pieces of meat and of 

 hard-boiled egg are softened within twelve hours; and they disappear almost 

 entirely after twelve hours more : the fluid acquires a peculiar sourish odour, 

 which is not, however, of a putrescent character. When the fluid is not 

 acidulated, it is found to have no more solvent power than simple water would 

 have. It was stated by Schwann, as the result of his experiments, that the 

 quantity of free acid remains the same at the end of the digestive process as it 

 was at its commencement ; whence he inferred, that the acid does not enter 

 into combination with the substances dissolved: but this was probably an 

 error, resulting from the weakness of the organic base with which the acid 

 combines. 



456. The active agent in the process appears to be an organic compound, 

 to which the name of pepsin has been given. The properties of this have 

 been investigated by Wasmann, who first succeeded in obtaining it in an 

 isolated state ;* his observations were made upon the mucous membrane of the 

 stomach of the Pig, which greatly resembles that of Man. When this mem- 

 brane is digested in a large quantity of water at from 85 to 95, many other 

 matters are removed from it besides pepsin ; but if this water be removed, and 

 the digestion be continued with fresh water in the cold, very little but pepsin 

 is then taken up. Pepsin appears to be but sparingly soluble in w r ater; when 

 its solution is evaporated to dryness, there remains a brown, grayish, viscid 

 mass, with the odour of glue, and having the appearance of an extract. The 

 solution of this in water is turbid, and still possesses a portion of the charac- 

 teristic power of pepsin, but greatly reduced. When strong alcohol is added 

 to a fresh solution of pepsin, the latter is precipitated in white flocks, \vhich 

 may be collected on a filter, and produce a gray compact mass when dried. 

 Pepsin enters into chemical combination 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. " In regard to the 

 solvent power of pepsin for coagulated albumen, it was observed by M. Was- 

 mann that a liquid which contains 17-10,000ths of acetate of pepsin, and 6 

 drops of hydrochloric acid per ounce, possesses a very sensible solvent power, 

 so that it will dissolve a thin slice of coagulated albumen in the course of 6 or 

 8 hours' digestion. With 12 drops of hydrochloric acid per ounce, the white 

 of egg is dissolved in 2 hours. A liquid which contains 3 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 dissolving 210 grains of coagulated 

 white of egg at a temperature 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 ebulli- 

 tion, 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, fibrin, 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 epider- 

 mis, horn, the elastic tissue (such as the fibrous membrane of arteries) do not 



* Graham's Elements of Chemistry, [Am. Ed. p. 695.] It is considered by Liebig, how- 

 ever, that Pepsin has no proper existence as such; and that the dissolving power of the 

 animal membrane is due to the state of decomposition, which has been induced in it by 

 exposure to air. It does not appear, however, that any other membrane than that of the 

 Stomach can undergo this change. 



