NUTRIENT MEDIA AND METHODS OF CULTIVATION. 



131 



process very little air re-enters the jelly, and colonies of even strictly 

 anaerobic bacteria wiU develop in the lower part of the tube. The 

 drawback is the difficulty encountered in examining the colonies, 

 and in preparing sub-cultures. For this purpose the tube 

 must be broken, or carefully warmed until the jelly can be 

 shaken out. 



Esmarch first prepares a roll culture, and when the gelatine film 

 has set, the tube is completely filled with liquefied gelatine which has 

 been cooled down almost to the temperature at which it solidifies. The 

 same difficulty arises as ^ 

 in the previous method, in 

 the examination of the 

 colonies. 



Bvichner places the 

 culture tube inside a much 

 larger tube containing a 

 small quantity of pyro- 

 gallic acid and closed with 

 a gutta-percha cap. The 

 pyrogallic acid absorbs the 

 oxygen, but the method 

 is not altogether success- 

 ful. 



The most satisfactory 

 plan is to exhaust the air 

 with an air pump, or to 

 substitute an atmosphere 

 of hydrogen which does 

 not affect the growth of 

 the bacteria. 



"Various forms of flasks 

 and tubes for cultivating 

 bacteria have been devised 

 which can be easUy con- 

 nected with an exhausting 

 apparatus, and readily 

 sealed by the flame of the blowpipe when the air has been removed. 



If hydrogen is employed the most convenient plan is to use 

 a Kipp's apparatus, from which the hydrogen is passed through 

 two bottles, one containing a solution of lead, to remove any 

 sulphuretted hydi-ogen, and the other pyrogallic acid, to intercept 

 any oxygen. 



Fig. 66.— Fkankel's Anaerobic Tube-ccltuke" 

 ' a,a. Glass tube through which hydrogen is 

 passed; 6, exit tube; c, india-rubber 

 stopper coated externally with paraffin 



(Fhanklan'd). 



