ANAEROBIC BACTERIA 171 



desiccator. The latter is covered and evacuated. The desiccator is then care- 

 fully turned so as to mix the alkali with the pyrogallol. Since this takes place 

 in the presence of traces of oxygen it browns only slightly. If the cover is not 

 tight, the admission of oxygen is readily indicated by the rapid browning of the 

 mixture. A beaker with water may be placed in the desiccator to prevent the 

 rapid drying out of the media. 47 



Various other methods for the physical or chemical absorption of the oxygen 

 from the atmosphere have been used; they are based upon the addition of organic 

 or inorganic substances, possessing a strong reducing power, to the medium or 

 outside of the medium in a gas-tight vessel. These include ferrous sulfate, sodium 

 sulfide, ammonium sulf-hydrate, sodium sulfite, ferro-ammonium sulfate, phos- 

 phorus; glucose, sodium formate, pyrocatechin, indigo-carmin; metallic iron and 

 zinc; various tissues, pieces of potato, carrot, fresh yeast, etc. These treat- 

 ments are often accompanied by a partial vacuum. The plates or tubes may be 

 placed in a container to which a quantity of freshly cut potatoes is added, then 

 covered with a bell jar. 



4. Replacement of air by an indifferent gas. Hydrogen, carbon dioxide, nitro- 

 gen, and other inert gases may be used for this purpose. A tube, 48,49 flask or 

 desiccator 50,51 supplied with a two-holed rubber stopper can be used for this 

 purpose. When all the air is replaced by the inert gas, the tubes are sealed. 62 



II. Cultivation in the presence of oxygen: 



5. Cultivation of anaerobes in the presence of aerobic organisms. This method 

 approaches nearest to what takes place in nature than any of the other methods. 

 By cultivating an anaerobic spore forming organism with an aerobic non-spore 

 former, like Bad. -prodigiosum, it is easy to obtain a pure culture of the former by 

 pasteurization. This method has only a limited application in the study of pure 

 cultures. Beijerinck 53 employed obligate aerobic bacteria to eliminate the last 

 traces of oxygen from the atmosphere. A combination of two of the above 

 processes may be used. 



The media used for the isolation and cultivation of anaerobic bacteria depend 



47 Rockwell, G. E. An improved method for anaerobic cultures. Jour. Inf. 

 Dis. 35: 581-486. 1924. 



48 Fraendel, C. tlber die Kultur anaerober Mikroorganismen. Centrbl. 

 Bakt. 3: 735, 763. 1888. 



49 Petri, R. J., and Maaszen, A. Ein bequemes Verfahren fur die anaerobe 

 Zuchtung in Flussigkeiten. Arb. K. Ges. Amt. 8: 314. 1893. 



60 Botkin, S. Eine einfache Methode zur Isolierung anaerober Bakterien. 

 Ztschr. Hyg. 9: 383. 1890. 



81 Novy, F. G. Die Plattenkultur anaerober Bakterien. Centrbl. Bakt. 16: 

 566. 1894. 



62 Richardson, A. C, and Dozler, C. C. A safe method for securing anaero- 

 biosis with hydrogen. Jour. Inf. Dis. 31: 617-621. 1922. 



63 Beijerinck, M. W. Oidium lactis, the milk mould, and a simple method to 

 obtain pure cultures of anaerobes by means of it. Proc. Sec. Sci. K. Akad. 

 Wettensch. Amsterdam, 21: 1219-1226. 1919. 



