258 METHODS OF ISOLATION 



be made upon solid media, for if carried out in fluid 

 media the aerobes multiplying in the upper layers of 

 fluid render the depths completely anaerobic, and 

 under these conditions the growth of the anaerobes will 

 continue unchecked. 



(b) When it is desired to separate a facultative 

 anaerobe from a strict anaerobe, it is generally suffi- 

 cient to plant the mixture upon the sloped surface 

 agar, incubate aerobically at 37 C., and examine 

 carefully at frequent intervals. At the first sign of 

 growth, subcultivations must be prepared and treated 

 in a similar manner. As a result of these rapid subcul- 

 tures, the facultative anaerobe will be secured in 

 pure culture at about the third or fourth generation. 



(c) If, on the other hand, the strict anaerobe is the 

 organism required from a mixture of facultative and 

 strict anaerobes, pour plates of glucose formate agar 

 (or gelatine) in the usual manner, place them in a 

 Bulloch's or Novy's jar, and incubate at a statable 

 temperature. Pick off the colonies of the required 

 organism when the growth appears, and transfer to 

 tubes of the various media. 



Incubate under suitable conditions as to temperature 

 and atmosphere. 



8. Animal Inoculation. Finally, when dealing with 

 pathogenic organisms, it is often advisable to inoculate 

 some of the impure culture (or even some of the original 

 materies morbi) into an animal specially chosen on ac- 

 count of its susceptibility to the particular pathogenic 

 organism it is desired to inoculate. Indeed, with some 

 of the more sensitive and strictly parasitic bacteria this 

 method of animal inoculation is practically the only 

 method that will yield a satisfactory result. 



