350 DIPHTHERIA. 



fragment is then fixed in a platinum loop by means of 

 sterile forceps, and a series of stroke cultures are made on 

 the surface of any of the media mentioned, the same por- 

 tion of the membrane being always brought into contact 

 with the surface. The tubes are then placed in the incub- 

 ator at 37 C, and, in the case of the serum media and 

 blood-agar, the circular colonies of the diphtheria bacillus 

 are visible in twenty- four hours. A small portion of a 

 colony is then removed by means of a platinum needle, 

 stained, and examined in the usual way, the characteristic 

 appearance of the organism being readily recognised. 



In cases where a suspicion arises that the organism 

 found is the pseudo-diphtheria bacillus, a broth containing a 

 trace of glucose should be inoculated and kept at the body 

 temperature for two days. If the reaction remains alkaline 

 the diphtheria bacillus may be excluded, but if it becomes 

 acid the organism may still be the so-called pseudo- 

 diphtheria bacillus. All the microscopical and cultural 

 characters must then be carefully observed, and its degree 

 of virulence may be ascertained by inoculating a guinea-pig, 

 say with i c.c. of a broth culture of two days' growth. 

 (See also pp. 345, 346.) 



