86 CULTIVATION OF ANAEROBIC BACTERIA. 
stand, and in the lower part of the large tube are placed ten cubic 
centimetres of a ten-per-cent solution of caustic potash, to which one 
gramme of pyrogallic acid is added. The absorption of the oxygen 
takes some time, but, according to Buchner, it is finally so complete 
that strict anaérobics grow in the small tube. 
In practice, cultivation in an atmosphere of hydrogen will be 
found the most convenient method, and for this any form of hydro- 
gen generator may be used. The writer is in the habit of using the 
form shown in Fig. 56. A perforation a quarter of an inch in 
diameter is drilled through the bottom of a wide-mouthed bottle. 
Some fragments of broken glass are then put into the bottle, form- 
Fia. 57, 
ing a layer two or three inches thick. Upon this is placed a quan- 
tity of granulated zinc. This bottle has a tightly fitting cork, 
through which passes a metal tube having a stopcock. The bottle 
is placed in a glass jar containing diluted sulphuric acid (one part 
by weight of sulphuric acid to eight parts of water). The acid, ris- 
ing through the perforation in the bottom of the bottle, when it 
comes in contact with the zinc gives rise to an abundant evolution 
of hydrogen, which escapes by the tube a@ when the stopcock is 
open. When this is closed the gas forces the acid back from con- 
tact with the zinc. To remove any trace of oxygen present the 
gas may be passed through a solution of pyrogallic acid in caustic 
potash. 
Evidently plates prepared by Koch’s method, or Esmarch roll 
