418 DIPHTHERIA 



is made on the surface of any of the media mentioned (p. 403), 

 the same portion of the membrane being always brought into 

 contact with the surface. More usually a swab taken from the 

 pharynx is smeared over the medium in a similar manner. ' The 

 tubes are then incubated at 37° C, and are ready for examina- 

 tion in eighteen to twenty-four hours. A representative sample 

 of the whole growth is obtained by rubbing a platinum loop 

 over the surface ; films are made from this, stained, and ex- 

 amined in the usual way, Neisser's stain being also applied. 

 Any doubtful organism should be tested by growing for two to 

 three days in glucose peptone water, tinted with neutral-red, to 

 which a few drops of sterile serum have been added to aid 

 growth. If no acid is produced the organism may be rejected ; 

 if acid is formed, animal tests should be carried out. For the 

 obtaining of a pure culture the telluric acid medium (p. 52) 

 will be found of great service. 



(c) Inoculation. — The bacillus in question should be grown in 

 bouillon for two 1 to three days, and then a guinea-pig inoculated 

 with 1 c.c. (This is the most suitable method, though it is not 

 strictly a test of pure virulence, the result being to some extent 

 due to toxin produced in the culture.) If the animal dies with 

 the characteristic lesions, further tests may be made with 

 smaller doses. The intra-cutaneous (p. 407) method mav also 

 be used. * For interpretation of results, vide p. 414. 



