Pepsin, a ferment found in gastric juice, capable, in the presence of weak acids, of converting proteids into peptones. For use in cases of indigestion it is introduced into the system as a medicine. The pepsin so used may be prepared from the inner surface of the stomach of calf, pig, or sheep. The stomach is laid open, washed, and scraped, the matter thus scraped off being spread on glass and dried at a gentle heat. A liquor with similar properties may be obtained by steeping the same part in glycerine. After eight days this liquor is strained, and for use a few drops may be taken in a glass of wine.