294 



The evaporation of the milk is not necessary, but when prepared from or- 

 dinary milk, the yoghurt remains more liquid, and as the acid formation is 

 equally strong as in evaporated material, there remains about 2.5,'o of the ori- 

 ginal 4.8/o milksugar, so that in this case the taste is much less sweet. 



If in the said way yoghurt has been prepared in the presence of air and 

 is re-inoculated into a new quantity of milk, then the result is yoghurt of the 

 same acidity as the first time. But after 3 or 4 transferrings difficulties arise 

 and only with great quantities of infection material further souring can be ob- 

 tained. The experiment succeeded much better when the yoghurt was prepared 

 in a quite filled stoppered bottle; the transferring can then be longer continued, 

 but I do not know whether this will do in the long run. Evidently the difficulty 

 here, too, is the right choice of oxygen pressure, whereby the inferred lactic acid 

 bacteria preserve their properties unchanged ; and this difficulty is still increased 

 by the presence of two different forms, with unequal optima as to temperature, 

 and probably as to oxygen pressure also. 



One of these forms is again a Lactococcus, the other a Lactobadllus. 



The former deviates somewhat from the common Laetocoecus, in as much as it 

 is more extended, reminding of short rods, and furthermore by possessing a higher 

 optimum as to the temperature whereby the growth is quickest, which optimum 

 proves nearer to 37 than to 30 C. Hence, this forms is as it were a transition 

 to a Lactobadllus. Isolation on milk agarplates was very easy, even at 30 C. 



As to the second species, the Lactobadllus proper of yoghurt, it was trouble- 

 some to grow its colonies on milk agar plates, but on malt extract agar it was 

 more easily obtained. In literature it has been named Badllus Massol by Grigoroff, 

 but I think that name superfluous as the characters correspond fairly well with 

 those of the kephir bacilli which also occur in our country ; for instance, as 

 has been observed before, in yeast and buttermilk. Sown in slightly soured milk 

 this Lactobadllus can produce the strong acid mentioned above, without the help 

 of other bacteria. Evolution of carbonic acid does not take place and the product 

 has a very pure taste, although a beginning of fat cleavage seems inevitable at 

 such a high amount of acid. 



Metchnikoff ascribes a very favourable influence to the use of yoghurt, 

 as it diminishes the phenomena of autointoxication starting from the intestinal 

 canal, and he explains this effect by accepting that the Lactobadllus, after passing 

 the stomach, continues active in the intestine, and checks 1 ) the formation of the 

 obnoxious products which derive from other bacteria species. I do not doubt but 

 this may be brought about by the lactic acid, but I think it highly improbable 

 that the presence of the lactic acid bacteria from the yoghurt themselves should 

 be required in the intestine. I think this conclusion is necessary, first because, 

 without the use of yoghurt or other soured milk preparations, there occur in the 

 intestine lactic acid ferments of different species, and second, because the con- 



') Quelques remarques sur le lait aigri. Remy, Paris 1907. In this paper Metcli- 

 nikoff gives many assertions but no decisive experiments. Besides, his bacteriological 

 elucidation, p. 26, is not clear. The elaborate and interesting work of Dr. A. Combe, 

 .'autointoxication intcstinale, Paris 1907, is neither quite convincing from a micro- 

 biological point of view. 



