APPLICATIONS OF LACTIC ACID FERMENTATION 101 



streptococci. As soon as the milk has coagulated, it is cooled in 



running water and placed on ice ; the production of acid must 



be stopped at the right moment, otherwise the Yoghurt will 



become too sour. Sometimes the milk is concentrated to half 



its original bulk before inoculation, in which case the product 



will be more nutritious, but less refreshing than that prepared 



from unconcentrated milk. It will then correspond in com- 



position to Yoghurt made from Buffalo milk, which is con- 



sidered particularly choice. According to Metschnikoff, the 



Yoghurt rod bacteria inhibit the growth of the intestinal putrefactive 



organisms to a greater extent than do the other lactic acid bacteria, 



and thus prevent digestive troubles, rheumatism, calcareous 



growths, and, generally speaking, prolong life. Centenarians are 



said to be more numerous 



in Bulgaria than in other 



countries, and considering 



the claims which were made 



on its behalf, it is no wonder 



that Yoghurt at one time 



came into demand in all civil- 



ised countries. People ate 



not only Yoghurt, but Yog- 



hurt tabloids, which fre- 



quently contained no living 



lactic acid bacteria, but 



always Bacillus mycoides or 



other sporing organisms. To 



what extent Thermobacterium FIG. 61. Bacterium bifidum, distinctly 



bulgaricum Can become accli- 



matised to the conditions of 

 the alimentary canal of man and animals is extremely doubtful 1 . 

 The author has never succeeded in finding this organism in 

 the faeces of adults, even after large daily doses of Yoghurt. 

 Neither was it possible to find this easily recognisable rod form 

 in the faeces of an infant constantly fed on milk which had 

 been inoculated with a few drops of Yoghurt 2 . However, by 

 inoculating a little of this faeces into milk which was kept at 45 C., 

 the Yoghurt rod was obtained as a pure culture. A more rational 

 procedure would be to introduce into the intestine those lactic 



1 Thus Hull and Eettger found that Thermobacterium bulgaricum could 

 not be acclimatised in the alimentary canal of the white rat (" Centralblatt 

 f. Bakteriologie," 1 Abt., 1914, Bd/LXXV., p. 219). 



2 A slight addition of Yoghurt has an aperient action, and it is certainly 

 more harmless than other aperients. The thermobacteria seem to be able 

 to thrive in the stomach of young animals as long as they are fed on milk 

 alone, and where the production of hydrochloric acid is lower than later on. 



branched. From faeces of bottte-fed 

 infant. X 1,000. 



