8o PRACTICAL BACTERIOLOGY. 



aboTOj only inoculation is more difficult. The nutrient 

 medium, which only occupies about one-third of the 

 test-tube, is boiled in order to expel the air, and then, 

 just as it has hardened, is inoculated. Sterilised oil is 

 then poured in, until the test-tube is nearly full, in 

 order to shut out the air. This method, however, is 

 not very much to be recommended. 



Species which are not strictly anaerobic may be 

 cultivated on plates, if the gelatine is covered with a 

 large sheet of mica just as it is solidifying. For strictly 

 anaerobic bacteria this method does not answer, as 

 too much oxygen gets into the gelatine before the 

 mica is put on, owing to the large surface it exposes 

 to the air. 



If nothing but the further cultivation of anaerobes is 

 desired, this can be effected in a considerable quantity 

 of bouillon, to which it is best to add 1 per cent, of 

 grape sugar. In this manner, however, the charac- 

 teristic appearances seen in the solid medium cultures 

 are lost, and it is not so easy to discover any accidental 

 impurities, on which account cultivations in bouillon 

 are hardly to be recommended. 



Finally, anaerobes can also be cultivated in the 

 hanging drop, if the following method is adopted : 

 cover-glasses and slides are prepared in the manner 

 described in the preceding chapter, inoculation is 

 performed, and the cover- glass is laid on, a drop of 

 concentrated caustic potash solution being placed at 



