MIXED CULTURES. 87 



and Micrococcus acidi paralactici. Fuller information concerning 

 the individual behaviour of these two Schizomycetes will be found 

 in subsequent paragraphs, which we will here anticipate in respect 

 of the fact now coming under consideration, viz., that the first- 

 named bacillus yields, in nutrient solutions containing cane-sugar, 

 the following fermentation products : hydrogen, carbon dioxide, 

 normal butyric acid, and inactive lactic acid. On the other hand, 

 Micrococcus acidi paralactici forms, almost exclusively, optically 

 active paralactic acid, and that, too, in a quantity almost identical 

 with the theoretical yield from the sugar eliminated. If, now, 

 both these organisms be cultivated together in the nutrient solu- 

 tion aforesaid, fermentation proceeds much more rapidly, and the 

 final products consist not only of the already mentioned substances 

 (yielded by the organisms singly), but also of a large amount of 

 normal butyl-alcohol. This substance, therefore, owes its pro- 

 duction in this case to the co-operation of two species of bacteria, 

 neither of which singly is capable of such power. 



Interesting as this fact, that new fermentation products can be 

 formed by the association of organisms, may be, the following one, 

 which was first established by BURRI and STUTZER (I.), is so in a 

 still greater degree. In this case two organisms are concerned, 

 neither of which is capable singly of liberating nitrogen from 

 nitrates; but, when acting conjointly, they decompose the same 

 nutrient medium with violent disengagements of gas. The one 

 organism is the Bacterium coli commune, already mentioned, and 

 very abundant in human faeces and that of domestic animals, 

 whilst the second microbe was named by the above-named natura- 

 lists Bacillus denitrificans I. A bouillon containing three grams of 

 sodium nitrate per litre, inoculated with both these organisms and 

 then maintained at 32 C., began to disengage gas in a short time, the 

 nitric acid in the nitrate being reduced to nitrogen so completely 

 that, even at the end of forty-eight hours, the extremely delicate 

 test with di-phenylamine-sulphuric acid gave only negative results. 



Apart from the purely scientific interest excited by these facts, 

 new vistas are also opened up in a practical sense. Up to the 

 present, investigators have contented themselves with the examina- 

 tion of the transformation products resulting from the pure cultiva- 

 tion of single species of bacteria. In future researches, however, 

 the question whether or not a species can be spurred on to more 

 extended activity by the collaboration of a second, so as to give 

 rise to the development of powers which, without such stimulant, 

 would remain unobserved and unutilised, cannot be neglected. 



This claim is not restricted to the domain of schizomycetic 

 fermentation, but applies also to the ferments of the Eumycetes 

 class. The mode of action exhibited by mixed cultures of dif- 

 ferent species of yeasts is of great importance in brewery and 

 distillery practice. In this connection we are already in posses- 

 sion of several studies by E. Ch. Hansen and others, the results of 

 which will be considered in a subsequent section. 



