Such an enzyme is the pepsin of the stomach of the higher animals.
A third enzyme, the trypsin of the pancreas, possesses the power of both pepsin and erepsin.
It is not quite certain whether a true pepsin exists in plants, but many trypsins have been discovered, and one form of erepsin, at least, is very widespread.
Substances obtained from animals include gland secretions, pepsin and other ferments, musk, cod-liver oil, &c., and to these may be added various antitoxins.
It is much more powerful than carbolic acid in its inhibitory action upon unorganized ferments such as pepsin or ptyalin.