THE BIOLOGICAL ACTIVITIES OF BACTERIA 50 



In the industrial employment of yeasts for fermentative pur- 

 poses, it is necessary to work with specific strains, and in scien- 

 tifically conducted vineyards, breweries, and distilleries the study 

 and pure cultivation of the yeasts form no unimportant part of 

 the work. Certain, races of yeasts are more uniform in their fermen- 

 tative powers than others, and the by-products formed by some 

 races differ sufficiently from those of other races to cause material 

 differences in the resulting substances. In the wine industries, 

 the yeasts differ much from one another according to climatic and 

 other environmental conditions. In vineyards, natural inoculation 

 of the grapes occurs by transportation of the yeast from the soil 

 to the surface of the grapes by wasps, bees, or other insects, through 

 whose alimentary canals the microorganisms pass uninjured. In the 

 autumn the yeast is returned to the soil by falling berries and 

 remains alive in the upper layers of the ground throughout the 

 winter months. In actual practice this natural yeast inoculation is 

 not depended upon, but pure cultures of artificially cultivated yeasts 

 are employed for inoculation. In some of the wine-growing coun- 

 tries these are supplied by special government experiment stations. 



Denitrifying Bacteria. Nitrogen is most readily absorbed by 

 plants in the form of nitrates. These are furnished to the soil chiefly 

 by the protein decomposition induced by the proteolytic bacterial 

 enzymes. It is self-evident, therefore, that any cleavage which 

 reduces nitrogenous matter beyond the stage of nitrates, to nitrites 

 and ammonia, detracts from the value of the nitrogen as a food 

 stuff for plants, and the eventual setting free of nitrogen in the 

 elementary state renders it entirely valueless for any but the 

 leguminous plants. 



Nevertheless, this process of nitrogen waste or denitrification 

 is constantly going on in nature. In the course of ordinary decom- 

 position, there is a constant reduction of nitrogenous matter to 

 nitrites and salts of ammonia, actively taken part in by a host of 

 bacteria, as many as 85 out of 109 investigated by Maassen 17 being 

 found to possess this power. This, however, is not nearly so harmful 

 a source of nitrogen waste as the process technically spoken of as 

 true denitrification, in which nitrates are reduced, through nitric 

 and nitrous oxides, to elementary nitrogen. 



This phenomenon, more widely spread among bacteria than at 



" Maassen, Arb. a. d. kais. Gesundheitsamt, 1, xxviii, 1901. 



