To physiologists we are indebted for the discovery and development of the scientific preparation of digestive ferments or enzymes and the predigestion of food outside of the body. The composition of the various digestive ferments and their action in general have been understood for a long time, but it is only within the last two or three decades that the use of these organic bodies has been made practicable on a large scale for rendering food more digestible or assimilable by invalids, and the whole question of artificial digestion of foods is one which is receiving more and more careful attention and thorough study. The subject may be said to be yet in its infancy, and it is highly probable that the extensive researches which are being conducted by so many investigators at the present day will yield even more practical and important results than those already attained. The use of predigested food at present forms an indispensable adjunct to the treatment of a large number of serious diseases, both acute and chronic, especially those which concern the alimentary canal, and the methods of infant and invalid feeding have been practically reorganised by it.

The different ferments which can be used for increasing the activity of digestion within the body or for partially digested foods outside of the body are principally diastase, pepsin, and extracts of pancreatic juice, which are usually called "pancreatin," and which are compounds of several substances. Besides these there are several vegetable ferments, such as papain from the American papaw, and ferments are present in the juice of the pineapple, and the century plant or agave.