As some kinds of soured milk, such as “varenetz,” “yahourth,” “leben,” etc., are prepared from boiled milk, it might be supposed that they fulfil the conditions necessary for prolonged use. A closer examination, however, makes us reject them. Boiled milk, to make it undergo the lactic fermentation properly, must have added to it a prepared ferment. What is necessary is not merely rennet, as was formerly supposed, but a number of organised ferments, that is to say, microbes. In the preparation of these soured milks, a leaven is employed, one of the names of which is “Maya,” and which contains not only lactic microbes, but several others. MM. Rist and Khoury[143] have come to the conclusion that the Egyptian “leben” contained a flora composed of five species, three of which are bacteria and two yeasts. The bacteria produce lactic acid and the yeasts alcohol. Although the result is that “leben” is a nearly solid substance, whilst kephir is a liquid, the two are closely similar. In both cases we have to do with coincident lactic and alcoholic fermentations, and my remarks regarding kephir apply equally well to the Egyptian “leben.” Through the agency of Prof. Massol of Geneva, I have obtained a specimen of the Bulgarian “yahourth.” Working with his pupil, M. Grigoroff, M. Massol[144] has isolated several microbes from this milk, amongst these being a very active lactic bacillus. The same soured milk has been studied in my laboratory by Drs. M. Cohendy[145] and Michelson. They found in it a very powerful lactic ferment, which has been named the Bulgarian bacillus. This was the microbe employed in the experiments of M. Bélonowsky, to which I have already referred. More recently, it has been carefully investigated from the chemical point of view by MM. G. Bertrand and Weisweiler[146] at the Pasteur Institute. It proved to be an extremely active producer of lactic acid, supplying 25 grammes per litre of milk. The other acids which this bacillus produces, such as succinic and acetic acids, are formed only in very small quantities (about 50 centigrams a litre). Formic acid is produced only in traces. On the other hand, the Bulgarian bacillus forms neither alcohol nor acetone, two frequent products of bacterial fermentation. The bacillus also differs from other lactic ferments inasmuch as it has no action on albuminoids (casein, etc.), nor on fats. All these qualities make the Bulgarian bacillus much the most useful of the microbes which can be acclimatised in the digestive tube for the purpose of arresting putrefactions and pernicious fermentations, such as the butyric fermentation.