The general interpretation of the benefits gained from the use of lactic acid ferments is that they depend solely on the action of the lactic acid which they produce in preventing the multiplication of the microbes which cause putrefaction. Recent investigations made by Dr. Bélonowsky, at the Pasteur Institute, show that a lactic ferment isolated from yahourth and described as the Bulgarian bacillus owes its antiseptic powers not only to lactic acid but to another substance which it secretes. Dr. Bélonowsky has studied the effects of this bacillus upon mice, by adding to their previously sterilised food quantities of this lactic microbe. As control experiments he fed other mice on food to which lactic acid had been added in quantities corresponding to the quantity produced by the Bulgarian bacillus, or which had been mixed with other kinds of bacilli. Another set of mice were given normal food without the addition of either microbes or lactic acid.
Out of these groups of mice, those which had been given the Bulgarian bacillus thrived best and had most progeny. Their droppings showed fewest microbes, particularly microbes of putrefaction.
The next stage in Dr. Bélonowsky’s experiments was to feed mice not with living quantities of the Bulgarian bacillus, but with cultures which had been sterilised by heat (120°-140° Fahr.). These mice lived as well as those to which living cultures had been supplied, and notably better than those supplied with pure lactic acid. It is evident therefore that there is some other product of this bacillus which favours life by preventing intestinal putrefaction.
Dr. Bélonowsky showed, moreover, that the Bulgarian bacillus cures a special intestinal disease known as mouse typhus.
The experiments which I have described show that intestinal putrefaction is to be combated not by lactic acid itself, but by the introduction into the organism of cultures of the lactic bacilli. The latter become acclimatised in the human digestive tube as they find there the sugary material required for their subsistence, and by producing disinfecting bodies benefit the organism which supports them.
From time immemorial human beings have absorbed quantities of lactic microbes by consuming in the uncooked condition substances such as soured milk, kephir, sauerkraut, or salted cucumbers which have undergone lactic fermentation. By these means they have unknowingly lessened the evil consequences of intestinal putrefaction. In the Bible soured milk is frequently spoken of. When Abraham entertained the three angels he set before them soured milk and sweet milk and the calf which he had dressed (Genesis xviii. 8). In his fifth book, Moses enumerates amongst the food which Jehovah had given his people to eat “Soured milk of kine and goat’s milk, with fat of lambs and rams of the breed of Bashan, and goats with the fat of kidneys” (Deut. xxxii. 14).[138]
A food known as “Leben raib,” which is a soured milk, prepared from the milk of buffaloes, kine or goats, has been used in Egypt from the remotest antiquity. A similar preparation known as “yahourth” is familiar to the populations of the Balkan Peninsula. The natives of Algiers make a kind of “leben” not identical with the Egyptian form.
Soured milk is consumed in great quantities in Russia in two forms, “prostokwacha,” which is raw milk spontaneously coagulated and soured, and “varenetz,” which is boiled milk soured with a yeast.
The chief food of many natives of tropical Africa consists of soured milk. The staple diet of the Mpeseni is “a curdled milk, almost solidified.” “Meat is eaten only on ceremonial occasions.” According to Foà, a tribe of the Nyassa-Tanganyika plateau, like the Zulus, take milk only in the form of a raw cheese mixed with salt and pepper.
Dr. Lima of Mossamedes, in West Africa, has told me that the natives of many regions south of Angola live almost entirely on milk. They employ the cream as an ointment for the skin, whilst the milk, soured and curdled, is their staple food. M. Nogueira reported the same circumstances nearly fifty years ago after his journey in the province of Angola.