RELATION OF MICROORGANISMS TO SPECIAL DAIRY PRODUCTS 511 



by the Bulgarian tribes for a long time. Some years ago it was studied 

 and brought to public notice by the investigations and writings of 

 Metchnikoff,* who was struck by the longevity of the tribes using this 

 product as a part of their regular diet. As a result of his investigations, 

 Metchnikoff has advanced his theory regarding the antiseptic power 

 of certain strains of lactic bacteria in the digestive tract. His theory 

 is that certain species or types of bacteria which are able to resist 

 the action of the stomach and can, therefore, pass through into the 

 intestines have the power of checking the growth of the putrefactive 

 bacteria existing there and thereby prevent the production and ab- 

 sorption of bacterial toxins which cause autointoxication. As a result 

 of his experiments, Metchnikoff came to the conclusion that the acid 

 organism (Bad. btilgaricum)^ found in yahourth was able to establish 

 itself in the intestinal tract and produce enough lactic acid to hold 

 in check the putrefactive processes which otherwise exist there. 



Yahourth is made by the Bulgarians in skin bags in the same way 

 that the Russian tribes prepare kumyss. It is similar to the other fer- 

 mented drinks already described in the fact that it is produced by a 

 mixed flora of microorganisms. At least one yeast is present and two 

 or more species of bacilli capable of producing lactic acid in relatively 

 large amounts. These two organisms are known as Bad. bulgaricum 

 and Bacillus paraladicus. Herter states that Bad. bulgaricum is 4/i to 

 6ju in length by i/z in width and grows singly or in pairs and occasionally 

 in chains. It stains with ordinary aniline dyes and by Gram's method. 

 It grows with difficulty on ordinary laboratory media and is therefore 

 hard to obtain in pure cultures. These organisms produce a much 

 higher percentage of acid than the common Bad. lactis acidi and also 

 grow at a much higher temperature. 



This makes it possible to secure it in practically pure cultures by 

 growing it in milk at a high temperature. Grown in pure cultures, the 

 Bad. bulgaricum will produce from i to 2 or more per cent of acidity. 

 It grows well at temperatures between 37 and 40 and even higher. 

 Recently a number of fermented milk drinks have been put upon the 

 market which have evidently been derived from the yahourth. These 

 are sold under such trade names as zoolak, vitalac, yogurt, fermenladyl, 

 etc. The flora of these preparations appears to be practically the same 

 as that of the original yahourth. 



*E1., Metchnikoff, Prolongation of Life. 



t Hastings has found this organism also common in co\\'s milk in this country. 



