48 BACTERIOLOGICAL DIAGNOSIS. 



thionin on to the film and allow it to act for 2 minutes. 

 Wash under the tap. 



Dry by pressing carefully with strips of blotting-paper 

 and then in the flame. Place a drop of balsam upon 

 the film and apply a cover-glass. 



Prepare a second film and stain by Gram's method 



(p. 32). 



The films are now examined microscopically (see 

 p. 34). We shall defer the description of the points 

 upon which a diagnosis is to be based until we deal 

 with the examination of cultures. 



CULTURAL METHODS. 



The diphtheria bacillus grows best at or near the 

 body temperature (about 37 C.) and flourishes on 

 almost all culture media. But agar is scarcely ever 

 used in growing it for diagnostic purposes : this 

 medium serves well for the cultivation of a great 

 many organisms, some of which are almost always pre- 

 sent in the mouth, so that cultures made upon it are 

 usually very impure. We use a medium which permits 

 the development of the diphtheria bacillus and inhibits 

 that of most other organisms. The best are ascitic 

 agar and solidified blood-serum. 



The method in which the medium is inoculated is as 

 follows : The tube of culture medium and the tube 

 containing the swab are held side by side between the 

 index and middle fingers of the left hand, the mouths 

 of the tubes pointing to the right and slightly down- 

 wards. The plug of the culture tube is then singed, 

 removed by means of a pair of forceps, and placed be- 

 tween the ring and little fingers of the left hand. The 



