This section is from the book "Practical Dietetics With Special Reference To Diet In Disease", by William Gilman Thompson. Also available from Amazon: Practical Dietetics with Special Reference to Diet in Disease.
The object of peptonising milk is to complete a portion of the digestive process outside of the body, and thereby relieve the alimentary canal of this work. A great variety of preparations of pepsin, peptonising powders, etc., are offered in market.
In general they are pure, but they vary somewhat in rapidity and strength of action. The powder may be added some time before the milk is swallowed, and in this event it can only act in conjunction with dilute hydrochloric acid. If added to the milk at the time of swallowing, the normal acid of the gastric juice supplies the proper reaction.
The process of artificial peptonising consists in adding one of the numerous preparations of pepsin obtained at the pharmacist's to fresh acidulated milk, and allowing it to stand in a bottle immersed in warm water at approximately the body temperature. A fermentation results in which the casein is more or less completely converted into albumoses.
If the process be too long continued, further fermentation results, and the milk becomes very bitter. It is therefore checked after a few minutes, either by boiling the milk, which has the effect of destroying the pepsin, or by keeping it upon ice until ready for use, which inhibits the action of the ferment.
Either peptonised or pancreatinised milk may be prepared in quantity for use by infants or invalids during the day, and if there is an ice chest to keep it in, it is better to do so, for then it is more uniform in composition. If ice is not at hand, the preparation should be freshly made for use each time, otherwise it will become bitter and spoil.