METHODS USED IN CULTIVATION OF BACTERIA 



155 



carried out two or three times. After the last exhaustion, the glass tube 

 in the bottle connecting it with the jar is pushed down into the fluid, 

 and the vacuum will draw the sodium hydrate solution into the bottom 

 of the jar, dissolving the pyrogallol, which will then absorb any traces of 

 free oxygen remaining in the jar. Hydrogen is again introduced and the 

 jar closed. If exhaustion of oxygen has been sufficiently thorough, 

 the pyrogallic solution in the bottom of the jar will remain light brown. 



A simple method for the separation of anaerobes in plates without the 

 use of hydrogen or of specially constructed jars, may be carried out as 

 follows l : The apparatus used consists of two circular glass dishes, fitting 

 one into the other as do the halves of a Petri dish, and similar to these 

 in every respect except that they are higher, and that a slightly greater 

 space is left between their sides when they are placed together. The 



From hydrogen 

 generator 



To exhaustion 

 pump 



FIG. 39. APPARATUS FOR COMBINING THE METHODS OF EXHAUSTION, HYDROGEN, 

 REPLACEMENT, AND OXYGEN ABSORPTION. 



dishes should be about three-fourths to one inch in height, they need 

 be of no particular diameter, although those of about the same size as 

 the usual Petri dish are most convenient. An important requirement 

 necessary for the success of the method is that the trough left between the 

 two plates, when put together, shall not be too broad, a quarter of an 

 inch being the most favorable. 



Into the smaller of these plates the inoculated agar is poured exactly 

 as this is done into a Petri dish in the ordinary aerobic work. Pro- 

 longed boiling of the agar before plating is not essential. When the agar 

 film has become sufficiently hard on the bottom of the smaller dish, the 

 entire apparatus is inverted. The smaller dish is now lifted out of the 



Zinsser, Jour. Exp. MecL, viii, 1906. 



