CULTIVATION OF ANAEROBIC BACTERIA. 79 



angles, and connected with the hydrogen-generating 

 apparatus. After four or five minutes the air is ex- 

 pelled from the test-tube, which is then, whilst still 

 held over the stream of hydrogen, quickly closed with 

 a tight, well-fitting india-rubber stopper, which is with- 

 out holes and which has been sterilised in the usual 

 manner. Whilst the tube is still kept upside-down 

 its stopped-up end is immersed in a dish of liquefied 

 parafiin, prepared beforehand, in order to close up any 

 fissures between the tube and its stopper, and thus to 

 render the apparatus quite air-tight. 



The success of these cultures of strictly anaerobic 

 species depends chiefly on the exactitude, skill and 

 quickness of the operator ; they easily fail if any pre- 

 caution has been neglected. With careful manipula- 

 tion, however, so very little oxygen can remain in the 

 nutrient medium, that there is no doubt but that only 

 very few anaerobes are hindered by it in their develop- 

 ment. If preparations to be examined with the 

 microscope are to be prepared, it is certainly best to 

 employ this method ; but if permanent cultures of 

 anaerobes are to be made, it is too inconvenient, and 

 it is therefore best to make the cultures in deep 

 layers of solid media, as described before. 



In many cases, especially when it is only desired to 

 observe the characteristic growth of a species of 

 anaerobes in gelatine or agar-agar, another method 

 may be adopted, which is nearly as successful as the 



