172 SEVENTH REPORT. 



The medium Avas rendered alkaline to litmus, tnbed, sterilized and in- 

 oenlated as before. 



The results in these cultures were unsatisfactory. In the first place, 

 the media proved unfavorable for some of the organisms, eight of which 

 showed no growth in 24 hours, and others only slight growth. Further- 

 more the dark color of the media prevented a sharply marked reaction^ 

 even in the most active indol producers, and in cultures in which only 

 a trace of indol Avas present its detection would be practically impos- 

 sible. Again, the more abundant groAvth genera'lly, in the tryptophan 

 Uschinsky medium, indicated that the tryptophan solution alone is not 

 a favorable medium for the cultivation of different types. This fact 

 alone served to thwart one of the first objects of the research, that is, to 

 prepare a medium in which efficacy and simplicity of preparation would 

 be combined. 



In a more extended comparative study of the use of Dunham's solu- 

 tion and sugar-free bouillon, the results obtained indicated that upon 

 the whole, there was little advantage in either medium over the other. 

 Under the same conditions some organisms produced more indol in 

 shorter time in Dunham's solution than in sugar-free bouillon; Avhile 

 others produced more in the latter than in Dunham's solution. The 

 sugar-free bouillon proved a more favorable medium for growth than 

 did the Dunham's solution, some organisms showing only slight growth 

 in the latter in twenty-four hours. 



On testing the sugar-free bouillon for tryptophan, a very much stronger 

 reaction was obtained than with ordinary bouillon. From this fact it 

 may be inferred that the usefulness of sugar-free bouillon as a medium 

 for indol detection, lies, not in the absence of sugar, but in the fact 

 that in the fermentation incident to the preparation of the medium, the 

 tryptophan group is split off from the proteid molecule and thus ren- 

 dered more readily accessible to attack by micro-organisms. 



There is unquestionably a decided advantage in the addition of 

 tryjitophan to culture media for the quick detection of indol production ; 

 but the length of time required in isolating it, precludes the practicability 

 of making general use of the substance in the preparation of media. 



