( Originally Published 1913 )
When milk remains for a time in open vessels, various forms of fungi fall into it from the air; among them, also, the Bacterium acidi lactici. In summer especially fermentation occurs at a temperature of from 20° to 30° C. The milk-sugar may, in a greater or less quantity, be transformed into lactic acid. Owing to this acidity, the milk coagulates and, by the agency of the lactic acid, the casein is rendered more digestible, especially when, as in kefir, this action is continued for two or three days. The longer this fermentation process lasts, the more the milk-sugar is fermented. In this way the sugar content of such milk, especially of a several days' old kefir, is considerably diminished, so that it is less injurious for diabetic patients than ordinary milk, with its rather high content of sugar.
When such a fermentation process occurs in milk through the action of special bacilli, instead of those of various kinds which enter it promiscuously from the air, a series of very valuable sour-milk products can be obtained. Kefir, for in-stance, is formed by two kinds of bacilli, one a yeast bacillus, the Saccharomyces mycodermia, and the other the Bacillus Caucasicus, which forms yellowish-white clumps. These tiny clumps may be bought in the drug-stores. Kefir of one day's standing contains only a very small amount of alcohol, which is formed by the decomposition of milk-sugar by means of kefir yeast ; on the second day there is more, and three days' old kefir contains still more. The milk is rendered much more digestible by this process. A portion of the casein is trans-formed into a soluble product, and the rest forms very tiny coagulated flakes. The older the kefir, the more hemialbumoses and peptones it contains. Kefir stimulates the digestion, and I have frequently obtained very good results by its use in cases where ordinary milk was not tolerated. The best results were observed in nervous dyspeptics and neurasthenics in general, who also gained considerably in weight. According to the experiments of Gilbert and Chassevant, the kefir made from skimmed milk is more easily digested. They found that a liter of such kefir of two days' standing was digested one hour earlier than a two-day kefir made from whole milk.
The koumiss prepared from mares' milk is very similar to kefir in its action, and is a beverage much liked by the Tartars and on the Steppes of the Kirgises. Already, in the time of the old Scythians, the antecedents of the Magyars, koumiss was a favorite drink, as stated by Herodotus. While in London I frequently drank koumiss made with cows' milk and the koumiss ferment in the Aylesbury Dairy, and found it very digestible, although I did not like the somewhat sweet-sour taste. Koumiss is quite expensive, and its curative properties are probably not any greater than those of kefir ; in fact, its greater alcohol content might be considered a disadvantage, for, while kefir contains only o.89 per cent. of alcohol, the quantity contained in koumiss is 1 per cent. more,—1.72 per cent. It contains 2.27 per cent. of albumin, 2.12 per cent, of fat, and 1.98 per cent. of milk-sugar. Its nutritive value is almost 100 calories less per liter than that of kefir.
The above-mentioned sour-milk products all have the property of combating the decomposition process in the intestine. When too much albumin is taken in the food, a portion of it may not be absorbed in the upper intestine. In the colon, then, where the intestinal flora is exceedingly abundant, its action causes decomposition, and products may be formed the absorption of which would result in injurious effects in the organism, It is in this process that sour milk and the other above-named products have such a favorable action. According to the experiments of Metchnikoff, the Bulgarian sour milk, jogurt (pronounced "jort," in the Bulgarian language), possesses this action to a much greater degree. Metchnikoff is inclined to attribute the longevity of the Bulgarians, among whom many centenarians may be found, to the daily use of jogurt. This product forms one of the most infallible agents in causing a disinfection of the intestine, which action is produced by the lactic acid, as has been proven by the experiments of Leva in the Strauss Polyclinic in Berlin.
Yogurt is produced by the aid of the maja bacilli. The milk is first cooked for a long time, about two hours, so that it thickens and loses about one-fourth of its amount; it is then cooled to about 40° or 450 C. The maja is then added and it is allowed to ferment at 450 C. In about five hours the milk is coagulated. It has a very sour taste. Some of my patients do not much like it, and it is not always well tolerated, as it very frequently causes acid eructations and fermentation in the intestine; for this reason its use—as well as that of the other sour-milk products—is not indicated in cases where there is acidity of the stomach. By many persons, however, it is well tolerated, and it then forms a very beneficial and healthy food. In addition to its disinfecting property, it also has a laxative action, and is likewise a pronounced diuretic. It is unfortunate that, as I have mentioned above, it is so frequently not well borne. It should, however, always be tried whenever its use is indicated, and should only be abandoned when its absolute intolerance has been proven.