ISOLATION AND CULTIVATION 103 



in the tubes. Place the label near the edge of the cover. 

 Wax pencils for marking glass may be used instead of the 

 gummed label. In making the dilutions it is important that 

 the wire loop should be flamed after making each transfer. 



Instead of inoculating the liquid media the material to 

 be inoculated is sometimes drawn by means of a platinum 

 wire over the surface of the medium after it is solidified in 

 the Petri dish. These are spoken of as streaked cultures. 



Inoculating animals. With the pathogenic bacteria such 

 as those of swine plague it is often easier to inoculate sub- 

 cutaneously a susceptible experimental animal with the 

 medium containing the organism. By this method the 

 saprophytic bacteria which might grow vigorously on the 

 media are destroyed in the tissues of the animal, but the 

 pathogenic species will in proper time kill the animal. From 

 the organs of the dead animal the organism can be recovered 

 ori suitable media usually in pure culture. In certain cases, 

 such as tuberculosis, it is almost necessary to make inocula- 

 tions in this way and to procure the culture on suitable media 

 from the organs of the diseased animal. In tetanus, espe- 

 cially when this organism is to be isolated from soil contain- 

 ing it, it is necessary to inoculate a susceptible animal 

 such as a guinea pig in order to procure a pure culture. 



THE CULTIVATION OF ANAEROBIC BACTERIA. 



Certain bacteria, such as the bacilli of tetanus and black 

 leg, can thrive in the absence of oxygen only. These bac- 

 teria will grow on the same kind of media as the aerobes 

 providing the atmospheric oxygen is removed. Various 

 methods have been introduced involving many devices for 

 the cultivation of these organisms. Notwithstanding this 

 fact our knowledge of the anaerobic bacteria is as yet very 

 limited. While rapid progress has been made along the line 

 of the aerobic species, a comparatively small number of the 

 anaerobic bacteria have been carefully studied and identi- 

 fied. The principles underlying the various methods that 



