38 IVAN C, HALL 



according to our best conceptions of the requirements. In con- 

 trast, the method of Lentz is open to the technical objection that 

 considerable absorption may occur before the seal is completed. 

 We have not tested the latter safficiently from a bacteriological 

 standpoint to justify any conclusion as to its real worth. The 

 dye test points to its suitability. 



In conclusion it is suggested that further studies are required 

 to show exactly to what degree of oxygen tension reduction the 

 decolorization of methylene blue under stated conditions corre- 

 sponds. Harvey's (1919) recent demonstration of the direct 

 relation between oxygen content and time of decolorization of 

 methylene blue in Schardinger's test and the interesting parallel- 

 ism between methylene blue reduction and luciferin formation 

 (1920) is significant in this regard, but one must not overlook 

 the great importance of the hydrogen ion concentration of the 

 test solution, and the effect upon this of atmospheric carbon 

 dioxide. 



Similar studies are equally needed in the investigation of the 

 oxygen relations of obligate anaerobic bacteria. 



SUMMAKY 



This paper reviews the literature on chemical criteria of anaero- 

 biosis, and undertakes a critical experimental survey of the sub- 

 ject in so far as it relates to the use of methylene blue for this 

 purpose. The mechanism of the decolorization of methylene 

 blue is studied in detail and shown to depend upon the inter- 

 action of alkaU and certain organic substances, notably carbo- 

 hydrates. A correspondence between Fehling's test and the 

 decolorization of methylene blue in alkahne solutions of various 

 carbohydrates is pointed out. 



It is shown that while there is a direct relation between the 

 amount of dye decolorized by heating and the amounts of alkali 

 and glucose, there is an inverse relation between the last two 

 factors in the test, so that an increase in one permits a decrease 

 in the other for the same result. 



Carbon dioxide, as well as oxygen, is shown to be an effective 

 factor in the recoloration of decolorized methylene blue. 



