SUGAIl IN THE NUTRIENT MEDIUM. 145 



sulphuretted hydrogen, mercaptan, carbonic acid, 

 hydrogen, marsh gas. 



But inasmuch as, in putrefaction of different nu- 

 trient media by different bacteria, the metabolic 

 products just mentioned are found, as a rule, only in 

 part and in extremely varying combinations, putre- 

 faction can hardly be defined more accurately with 

 chemical aids than is possible with the senses. 

 Hence I believe it is best to employ the term putre- 

 faction only in the general lay signification of every 

 foul-smelling decomposition of albuminoids (vide 

 Kuhn: A. H., XIII. , 1). 



9. Nitrification. 



The formation of small amounts of nitrous and 

 nitric acids is widely diffused among bacteria. 

 Heraeus (Z. H., 1, 193), who first investigated the 

 subject with pure cultures, found that in sterilized 

 urine which had been diluted fourfold very many of 

 the well-known bacteria form small amounts of nitrite 

 from urea or ammonium carbonate. These include 

 micrococcus pyogenes citreus, bacterium prodigi- 

 osum, typhi, coli, bacillus mycoides, anthracis, 

 vibrio pyogenes, and vibrio proteus. Various soil 

 bacteria also furnish nitrites. The addition of sugar 

 interferes with the production of nitrite from NH 3 

 until it is destroyed. The formation of nitrate was 

 not studied by Heraeus. Warington failed to find 

 nitrates in a study of twenty-four varieties in pure 

 cultures in nutrient solutions which formed nitrate 

 distinctly when infected by means of the soil (C. B., 

 VI., 498). 



According to more recent investigations nitrifica- 

 10 



