The Fermentation Tube 201 



As regards motility it is interesting to note that it is more 

 easily overlooked in bouillon cultures than when very recent 

 colonies on gelatin or agar are examined in the hanging drop. 

 There is moreover a considerable variation among cultures 

 from different sources as to this property of motility. There 

 are to be found all gradations from cultures in which a motile 

 form ma}^ be seen only after prolonged searching, to those in 

 which almost all individuals are in motion. As to the coagu- 

 lation of milk there is likewise some variation in this function. 

 Some years ago I isolated an unquestionable colon bacillus 

 from the feces of an infant, which failed to produce coagula- 

 tion of milk even after several weeks' sojourn in the ther- 

 mostat. The same may be said of some cultures from animals. 

 These facts show that the colon bacillus is by no means a well 

 characterized species and the question arises how shall the 

 various races be classified ? The same thoughts have been ex- 

 pressed by other writers especially by Gilbert and I<eon'°. I 

 believe that the properties of these races as manifested in the 

 fermentation tube will serve as the best basis for a classifica- 

 tion. 



If we take for our culture a bacillus isolated from human 

 feces and manifesting all the characters usually ascribed to B. 

 coli communis we shall observe the following phenomena in 

 the fermentation tube at 37° C. 



In glucose bouillon within twenty-four hours the entire 

 fluid has become clouded and a certain quantity of gas has ac- 

 cumulated in the closed branch. At the end of the second 

 day more gas has formed. At the end of the third day a trifle 

 more is present. After this very little if any is set free. The 

 cloudiness promptly subsides and all growth is apparently at 

 an end. The fluid in the bulb will be found markedly acid. 

 This acidity is undoubtedly the cause of the sudden cessation 

 of activity, for if it be promptly neutralized with a sterile so- 

 lution of some alkali the fermentation starts again. It should 

 be stated that in these observations no " acid-binding " sub- 

 stance, such as CaCOj has been added to the fermenting fluid. 

 The following table gives in percentages of the tube length of 

 the closed branch (z. e., of the volume of the latter) the 

 amount of gas formed by B. coli from various sources : 



