SUGAR IN THE NUTRIENT MEDIUM. 141 



teria. At least Petri and Maassen found that, among 

 six varieties cultivated in bouillon containing 2.5-5 

 per cent peptone and 0.5 per cent saltpetre, there was 

 almost always a pronounced production of nitrites; 

 in one case, indeed, only ammonia was found. Rub- 

 ner (A. H. , XVI. , 62) found the production of nitrites 

 absent only in isolated cases. Among twenty-five 

 varieties Warington found that eighteen produced 

 nitrites. In our experiments with bacterium coli, 

 typhi, vulgare, bacillus anthracis, subtilis, vibrio 

 cholerse, the addition of sugar was not a disturbing 

 factor. At the end of three days the nitrite reaction 

 was equally pronounced, with or without the pres- 

 ence of one per cent grape sugar, in one per cent pep- 

 tone bouillon containing one-half per cent saltpetre. 



Nitrites are demonstrated in the following way : 

 After the tubes have remained for a few days in the 

 incubating chamber, some potassium iodide starch 

 solution (thin starch paste with one-half per cent 

 KI) and a few drops of sulphuric acid are added to 

 the nitrate bouillon (also to two uninoculated control 

 tests). The control tubes remain colorless or at the 

 most gradually acquire a very faint blue color, but 

 if nitrites are present, a dark blue to dark brownish- 

 red color develops. Small amounts of nitrite are de- 

 monstrated by metaphenylendiamin and somewhat 

 diluted sulphuric acid (yellowish-brown color) or 

 (most clearly) by a mixture of sulphanilic acid and 

 naphthylamin (red color) . ( Fide Dieudonne, A. G. 

 A., XL, 508). 



The demonstration of ammonia by the addition of 

 Nessler's reagent is permitted only upon inorganic 

 non-saccharine nutrient media. In bouillon Ness- 



