METHODS OF DIAGNOSIS. 375 



examining cases of diphtheria and making cultures from 

 them. 



(b) By making cultures. For this purpose a piece of 

 the membrane should be separated by forceps from the 

 pharynx or other part when that is possible. It should be 

 then washed well in a tube containing sterile water, most 

 of the surface impurities being removed in this way. A 

 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 incu- 

 bator 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 incubated at 

 36? C. The reaction should be tested after one and after 

 two days' growth. If it remains alkaline the diphtheria 

 bacillus may be excluded, but if it becomes acid the organ- 

 ism 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. 370, 



