2l8 PATHOGENIC BACTERIA. 



the melted gelatin or agar-agar rolled on its sides, as sug- 

 gested by Esmarch, if desired. 



Better than any of the preceding is the method of 

 Frankel, which removes the air and replaces it by hy- 

 drogen. Frankel prepares an ordinary Esmarch tube, 

 removes the cotton stopper, and replaces it by a carefully 

 sterilized rubber cork containing two tubes (Fig. 37). The 

 tubes are connected with a hydrogen generator, and the 

 gas is allowed to pass through until all the oxygen is 

 forced out and replaced by the hydrogen, after which the 

 ends of the tubes are sealed in the flame (Fig. 36). 



Liborius has designed a special tube for accomplish- 

 ing the same thing. 



Kitasato and Weil found the addition of 0.3-0.5 per 

 cent, of sodium formate to be of use in aiding the rapid- 

 ity of the development of anaerobic cultures. Liborius 

 found that 2 per cent, of glucose added to the culture- 

 medium also increased the rapidity of the process. 



The methods now generally employed by bacteri- 

 ologists for the anaerobic cultivations embrace all the 

 essentials of the foregoing methods. One of the best 

 arrangements for the purpose is that devised by Ravenel. 

 His inoculations are deeply made in culture-media as 

 free from air as possible. The tubes are loosely plugged, 

 and are placed in an air-tight chamber the bottom of 

 which contains pyrogallic acid — pyrogallic acid 1, solu- 

 tion of caustic potash 1, water 10. The apparatus is 

 connected by two tubes with an exhaust-pump on one 

 side, and with a hydrogen apparatus on the other, by 

 which means the atmosphere is exhausted and replaced 

 by hydrogen until only pure hydrogen remains, after 

 which the chamber is permanently sealed and the germs 

 allowed to grow. Such a chamber can be constructed to 

 hold a number of tubes or Petri dishes, yet not be too 

 large to be stood in an incubator. Whatever oxygen 

 may have escaped the exhaustion or have entered by the 

 process of leakage is at once absorbed by the pyrogallic 

 acid in the lower chamber of the apparatus. 



