SUGAR IN THE NUTRIENT MEDIUM. 143 



brownish-yellow color and prevents entirely the de- 

 monstration of indol. 



Demonstration of phenol: The culture, which is 

 made in non-saccharine bouillon, receives about one- 

 fifth its volume of hydrochloric acid and is then dis- 

 tilled. The distillate deposits flocculi with bromine 

 water, or assumes a violet color on the addition of 

 calcium carbonate and cautiously neutralizing, or of 

 neutral very dilute ferric chloride. 



Among sixty varieties examined we found indol 

 formed twenty-three times, and our findings agree 

 with those of Levandovsky (Deutsch. med. Wschr., 

 1890, No. 51). The chief indol producers are the 

 coli group in the widest sense glanders, diphtheria, 

 proteus, and the majority of vibriones. According 

 to Levandovsky the indol producers just mentioned, 

 with the exception of the vibriones, also form phenol. 

 We have tested the production of phenol only in bac- 

 terium coli and vulgare and found mere traces in five- 

 day cultures. 



7. Decomposition of Fats. 



Pure melted butter is not a nutrient medium for bac- 

 teria. The rancidity of butter is due to : (1) a purely 

 chemical decomposition of the butter by the oxygen 

 of the air, aided by sunlight (Duclaux, Ritsert) ; (2) a 

 lactic-acid fermentation of the milk sugar which has 

 been left over in the butter (vide v. Klecki, C. B., 

 XV. , 354) . Finally fat is attacked by bacteria and acid 

 is formed, if it is mixed with gelatin as a nutrient 

 medium (vide \. Sommaruga, Z. H., XVII., 441). 



