The Fermetitation Tube 193 



culties are not those which threaten the success of the work 

 and thejr count for little in important special investigations. 



The Reducing Action of Bacteria. — It has been known for 

 some years that certain bacteria have the power of abstracting 

 oxygen from compounds which hold it very loosel}-. It has 

 been customary among bacteriologists to demonstrate this de- 

 oxidizing or reducing activity by adding certain substances to 

 the culture fluid which are colored in the oxidized state but 

 which lose their color in the reduced state. Among the sub- 

 stances used are those mentioned above in the discussion of 

 the anaerobic properties of the tube, and the action of bacteria 

 correspond precisely to the action of heat in the presence of 

 glucose or peptone as has been already described. It is not 

 my intention to discuss this interesting phenomenon of reduc- 

 tion among bacteria excepting to call attention to the fermen- 

 tation tube in bringing it out. 



It will be remembered that when methylene blue, or indigo 

 carmine or litmus be added to peptone bouillon with or with- 

 out glucose so that the fluid becomes distinctly colored, and 

 the tubes steamed, the fluid in the closed branch becomes de- 

 colorized. If bubbles of air be tilted into the closed branch 

 and out again repeatedly, the color returns. Such tubes in- 

 oculated with any bacteria which are capable of growing in 

 the closed branch, if only to a slight degree, become within 

 24 hours completely decolorized, with the exception of a 

 shallow layer of fluid in the bulb. In the closed branch, for 

 reasons already given, the fluid remains indefinitely decolor- 

 ized. In the bulb the color returns when for any cause the 

 growth ceases and subsides. It is interesting to note that in 

 an ordinary bouillon culture of B. coli, the phenomena of re- 

 duction and oxidation could be witnessed for 15 days at the 

 end of which period the culture was rejected. The methylene 

 blue would lose its color within half an hour after it had been 

 re-oxidized by allowing air to bubble up into the closed 

 branch. If a small quantity of air was allowed to remain in 

 the closed branch, a stratum of blue fluid would remain at the 

 top of the fluid column near the air for some days, then dis- 

 appear completely, thereby indicating the complete consump- 



