CULTURE OF ANAEROBIC BACTERIA 79 



any of the gelatine to touch the cotton-wool plug. The 

 contents of the tube are allowed to set in cold water. On 

 incubating the tube at the room or higher temperatures as 

 the case may be, many organisms will be found to give 

 rise to the formation of gas, the bubbles of which will 

 become larger in size as growth increases. 



Culture of Anaerobic Bacteria. — In addition to the method 

 of studying anaerobic organisms by means of ' stab ' cul- 

 tures, many methods have been employed from time to 

 time, which depend upon the withdrawal of the oxygen 

 from the culture-tubes. 



The most simple method is to place the tubes, or plates, 

 under the receiver of an air-pump, and then withdraw 

 the air. 



Koch lays a thin sterilised plate of mica upon the 

 gelatine or agar plate ; this adheres closely to the surface 

 of the nutrient medium and excludes the oxygen. The 

 exclusion of air can be rendered more complete by running 

 melted wax round the edges of the plates. 



Bliicher and Botkin cultivate anaerobic organisms in an 

 atmosphere of an indifferent gas, such as carbonic acid 

 gas or hydrogen. 



Griiber effects the complete removal of oxygen by the 

 following means. The culture material is inoculated into a 

 culture-tube by means of Esmarch's method. The cotton- 

 wool plug is then pushed down the tube to about an inch in 

 depth ; and above is inserted an india-rubber stopper, which 

 must be well -fitting, and which is pierced with a hole 

 through which passes a glass tube. The air is then ex- 

 hausted from the tube by connecting the tube to an air- 

 pump. When this is done, the glass tube is sealed by 

 means of a blowpipe flame. The eggs of birds can also 

 be successfully used for the culture of many anaerobic or- 

 ganisms by the method which has been already described. 



