THE VITAL PHENOMENA OF BACTERIA. 117 



caused by a yeast of unknown species together 

 with a branched bacterium (Fig. 22). In the 

 preparation of the Eurasian beverage kumiss 

 out of mare's milk, and the drink called omeire 

 made out of cow's milk in southwestern Africa, 

 a bacterium and a yeast act together, producing 

 lactic acid and alcohol out of the lactose. A 

 true cooperative growth occurs also in the case 

 of the so-called kephir grains, a symbiotic 

 union of yeast and bacteria which together 

 accomplish a fermentation of the milk-sugar 

 of cow's milk with formation of lactic acid and 

 alcohol ; these kephir grains have been arti- 

 ficially cultivated in Caucasus for centuries. 

 According to investigations by Duclaux, Ada- 

 metz, Grotenfelt and Beyerinck, there are 

 also some yeasts which can form both alcohol 

 and lactic acid out of milk-sugar, and are 

 therefore able to produce unaided by any bac- 

 terium the alcoholic fermentation of milk. 



When different species, adapted for different 

 processes, follow one another in sequence the 

 phenomenon is called metabiosis. The end 

 members of this series, those which are best 

 adapted to the beginning and those best adapted 

 to the close of decomposition, are often in a sort 

 of opposition or antagonism. In the decompo- 

 sition of organic matter, such an opposition 

 outwardly exists between those organisms that 



