"2. The causative element of the curdling process of Dadhi is a streptothrix having characters similar to the Bacillus bulgaricus and Streptobacilli lebeni, and Bacillus caucasina and the Long Bacilli of Mazun, in (1) not growing in ordinary media; (2) producing a large amount of lactic acid in milk; (3) producing, besides coagulation of casein and splitting up the sugar of milk into lactic acid, no other change in milk; (4) not producing any indol, nor peptone, nor saponification of fat, nor formation of any gas.

"3. It differs from the above by showing peculiar pink-stained granules, when stained with methylene blue and showing peculiarly convoluted chains in glucose agar.

"4. The importance of the organism lies in the fact that, as in the case of Bacillus bulgaricus, it kills all pathogenic non-sporing germs and also destroys all proteolytic gas-forming bacilli in milk."

In the account of these investigations the following table is given, showing the amount of lactic acid produced by different lactic acid bacilli in one litre of milk, in terms of lactic acid—the culture being kept at 37° C.

Name of
the Bacillus		After
24
Hours		After
48
Hours		After
72
Hours		After
96
Hours		After
a
Week		Remarks
B. lactis ærogenes1.8...10.08......Observed by Hall and Smith
B. coli communis1.8...4.77......Observed by Hall and Smith
B. Bulgaricus12.8
-.4		16.5
-.4		20.2
-.4		...
...		22.0
-.4		Observed by Gabriel Bertrand and Weisweller; the initial acidity of the milk was 4.
Matzoon Long stäbschen B.10.812.0.........Observed by Düggeli
Streptobacillus lebenis2.61[34]............Observed by Rist and Khoury
Streptothrix dadhi
10.8
1.08
11.25
11.70
18.5
Medd. Coll. Calcutta

In different parts of the world sour milk is consumed in great quantities, and it is stated by Metchnikoff[35] that the chief food of the natives of tropical Africa consists of soured milk, and in Western Africa in the region south of Angola, the natives live almost entirely on this product, there being a difference in the curdled milks produced according to the nature of the microbial flora which is introduced.

It is stated[36] that in Servia, Bulgaria,[37] and Roumania there were 5000 centenarians living in 1896, and while many reasons are advanced for such an abnormal condition of affairs, it seems fairly certain that the sole reason why people in these districts live to such great ages is because of their mode of living and the fact that they live very largely on soured milk. The hygienic conditions throughout these countries are not such as would give the population in the towns and villages any special advantages in the prolongation of life, and while it may be stated that a pastoral and agricultural life are likely to contribute to longevity, these conditions would not account for a general tendency to live long in the countries referred to, more than in any other agricultural area. There are many countries throughout the world in which the pastoral and agricultural existence is general, but it has not been shown that in these countries life is prolonged. Hence the conclusion has been forced upon investigators that the reason is to be found not in the pastoral conditions, but in the habit which has existed from time immemorial of consuming sour milk as a principal article of diet.

There is no curtailment of the use of fermented milks in Eastern Europe, and the methods of preparation at the present day are those which have been carried out from time immemorial. A local observer states that in Bulgaria yoghourt is made in nearly every household, especially in the spring and summer. The method of preparation is very simple: The milk is boiled until a quarter of its volume has evaporated, it is then cooled to 45° C. and the ferment added. This ferment is a portion of the yoghourt of good flavour and is called "Maya" or "Zakvaska." The vases, a kind of earthenware pot, are enveloped in woollen stuff or sheepskin and placed in a warm place near the chimney. In ten hours the yoghourt is made, and it is preserved in a cold place. The great reputation that the yoghourt has acquired in Western Europe has caused this "Maya" to become an article of commerce. It is sent out by rail hermetically sealed in tinplate boxes. According to a Sophia chemist, the "Maya" is employed in the following manner: For a litre of milk it is necessary to take about 10 gr. of the ferment. This ferment is diluted with three times the amount of water and put into a bowl previously heated with hot water and dried. Into this bowl the milk, previously boiled and cooled to a temperature of 75° to 50° C., is poured; it is then covered over and put in a temperature of about 30° C., and, in default of a stove of constant temperature, the bowl is wrapped round with flannel or a plaid, and left to curdle for eight to ten hours. It is then ready for consumption. During winter, curdled milk keeps for several days, and in summer it becomes sour in from twelve to twenty-four hours.

A similar food to the yoghourt is prepared in the Balkan mountains from sheep's milk under the name of "Urgoutnik."[38] The milk is poured into a goatskin or sheepskin bag, and a little of the fermented milk added, and is then left for some hours in a warm place. The milk consumed is replaced by a fresh supply. In some of the Balkan countries, they are not content with the fermentation of the milk, they add a little alum, which, under the name of "typsa," is well known for this purpose. The milk attains such a solid consistency that it can be put into a cloth and carried to market.[39]

The various forms of sour milk which have been described in the foregoing pages may be said to be of the traditional kind, and with the light of modern knowledge, it has been possible to determine exactly what constitutes the active principle in use in the milk consumed in these countries, and, as we shall see, this principle has been applied so that, at the present day, a pure fermented milk may be obtained in any country, and there is every reason to believe that should such be adopted as a general article of food, it would contribute to the prolongation of human existence.