2 IVAN C. HALL 



reagent to serve both as a means of removing oxygen and as a 

 criterion of removal at the same time, so that the latter purpose 

 can be achieved only when combined with other means of oxj^gen 

 tension reduction. 



Fermi and Bassu (1904), using alkahne pyrogallol as a criterion, 

 encountered extreme difficulty in demonstrating complete anaero- 

 biosis. For example, they found that boiling media under 

 paraffine oil for over one hour does not prevent the darkening 

 of an alkali-pyrogallol mixture placed therein and a similar 

 statement was made respecting the passage of hydrogen and 

 carbon dioxide through media. It appears from my own experi- 

 ments that the colored compounds formed by the action of 

 oxygen upon alkali-pjTogallol mixtures are quite stable and the 

 reactions irreversible, for neither very weakly alkaline-solutions 

 which show only a trace of color with pyrogallic acid nor strongly 

 alkaline deep colored solutions can be decolorized by prolonged 

 boiling. Therefore the difficulty of making the mixture without 

 obtaining some coloi-ation and the further impossibility of remov- 

 ing it previous to actual test distinctly limit the practicability 

 of alkaline pyrogallol as a criterion of anaerobiosis, notwith- 

 standing its great value as a means of oxygen tension reduction. 



More extensive use has been made of substances which in the 

 absence of free oxygen are reduced to leucobases. Some of these 

 can be used, not only in media during the active growth of 

 organisms, but separately as well, for estimating the suitability 

 of special apparatus. Among such indicators may be mentioned 

 potassium ferro-ferro cyanid, litmus, indigo (sodium indigo 

 sulphonate) and methylene blue. 



Potassium ferro-ferro cyanid [(K2Fe (Fe Cye))] is of slight 

 historical, but no practical, miportance. It was used by Gunning 

 (1877) (1878) (1879) and is said to become colorless [FeaFe Cye] 

 when au' is eliminated. 



The earliest authentic reference to the bacteriological use of 

 Htmus appears to be that of Wiirtz (1892) who introduced htmus 

 lactose agar as a differential medium for Bad. coli and Bad. 

 typhosum. It was unpossible to confirm Novy's (1893) allusion 

 [copied by Hunziker (1902)] to Buchner (1885) and Cohen (?) 



