68 BACTERIA IN THEIR RELATION TO ONE ANOTHER 



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 loults. 



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 examination of the transformation products 

 iv>ulting from the pure cultivation 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 Eimiycetes class. The mode of action 

 exhibited by mixed cultures of different species of yeasts is of great importance 

 in brewery and distillery practice. In this connection we are already in pen- 

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

 considered in a subsequent section. 



