76 A MANUAL OF BACTERIOLOGY 



which passes through the rubber cork, is then connected 

 with a Kipp or other hydrogen- genera ting apparatus by 

 means of a rubber tube, and a current of hydrogen is 

 passed through the flask. The hydrogen bubbles through 

 the bouillon and escapes by the lateral tube. After the 

 gas has been passing for half an hour a small tube con- 

 taining mercury, c, is applied to the end of the lateral 

 branch, so that the open end just dips below the surface 

 of the mercury, and the tube, B, which passes through the 

 rubber cork, is sealed off in the blowpipe flame, care being 

 taken that all the air has been expelled from the flask 

 by a free current of hydrogen. The flask, with the capsule 

 of mercury applied to the end of the lateral branch, can 

 then be placed in the incubator. The mercury thus forms 

 a valve through which air cannot enter, while gases 

 formed by the growth of the organism have free exit. 



For large flasks, the lateral tube may be just bent down 

 and a little capsule of mercury attached. 



The addition of \ to 1 per cent, of sodium formate to 

 the culture media much simplifies anaerobic cultivation ; 

 the tetanus bacillus, for example, can be grown in formate 

 broth in a stoppered bottle without any elaborate pre- 

 caution for excluding the last traces of air. The sodium 

 formate should be added immediately before the last 

 sterilisation, not previously, or decomposition may occur. 

 Sodium sulphindigotate (0-3 per cent.) may be similarly 

 used. 



With such a broth, Dean's bottle may be used for 

 anaerobic cultivation. This consists of a bottle around 

 the neck of which a gutter for mercury is formed. A 

 glass cap loosely fits over the mouth of the bottle, and its 

 edge dips into the mercury in the gutter, thus sealing the 

 bottle. 



Plate cultivations. The method of plate culture is one 

 of the most important in bacteriology. It is used for 



