to be decisive would have to be conducted not merely on people in good health, but also on a suitable variety of digestive and nutritional disorders in which the bacterial conditions in the intestine, the state of metabolism and the general conditions of life are taken into account with the greatest care and judgment. Although I have for many years been interested in watching the influence of fermented milk on the human organism in various states of digestive derangement, and have accumulated many observations bearing on the question, my experience falls far short of what is necessary to establish final conclusions. In this communication, therefore, I do not offer any solution of the therapeutic problems pertaining to the use of fermented milks, but seek only to discuss critically, in the light of such information as now exists, some of the claims that have been made for the employment of these kinds of milk. I do this with the thought that a discussion of the various elements which should enter into the formation of a Judgment regarding the therapeutic value of milk subjected to lactic acid fermentation may prove helpful to those who have not given the subject much personal study and are therefore unable to analyze the problem in a way that is likely to serve as a practical guide.
There are five important kinds of effects referable to the action of fermented milks which must be considered in any judgment of the therapeutic effects of a milk which has undergone lactic acid fermentation. These are, first, the effects on the absorption of fats and proteins; secondly, the effects due to reduction of carbohydrates; thirdly, effects due to the presence of lactic acid; fourth, effects due to the bacteria used in lactic fermentation; fifth, effects due to a lowering of putrefactive decomposition. These latter effects, which are of the first importance in connection with any study of the action of fermented milk, are of course not entirely distinct from the others just mentioned, but stand related to each of these other factors. Owing to their prominence, however, it is desirable that they should be separately considered.
At present the influence of lactic acid fermentation upon absorption of the milk constituents is but little understood. The question relates especially to the absorption of fats and of proteins, for the carbohydrates of the milk are in large degree removed by the fermentative process, lactic acid, carbon dioxide and alcohol being the chief constituents resulting from the breakdown of the milk sugar. It is important that we should obtain exact data with regard to the absorption both of the fats and of the proteins, but, so far as I am aware, these do not at present exist. If it could be shown that the absorption of milk fat and of milk proteins is increased in health through the influence of lactic acid fermentation of any kind, this would be a distinct argument in favor of the use of such milk as an article of diet.