BACILLUS DIPHTHERIA 73 



tremities which results in the production of dumb- 

 bell and Indian-club shaped organisms. The proto- 

 plasm of the bacilli tends to segregation, so that the 

 phenomena of " polar staining " and "banding" of 

 the bacilli are extremely well marked, and can, 

 together with the other features mentioned, be 

 readily observed in the photographs. 



Metachromatism is also common, and the organism 

 is very prone to the production of so-called involu- 

 tion forms. 



If a swab which has been rubbed over the surface 

 of a diphtheritic membrane be then used to smear 

 the surface of a solidified blood-serum tube, and the 

 latter be kept at 37 C. for eighteen to twenty- 

 four hours, it will be found covered with colonies, 

 which in many cases consist almost exclusively of 

 Diphtheria bacilli. 



The method of bacteriological diagnosis of diph- 

 theria by culture, which is conducted as above, 

 depends on the extreme suitability of the medium 

 and the temperature for the growth of the diphtheria 

 bacillus, as compared with the other micro-organisms 

 generally associated with the specific bacillus. 



The colonies formed are discrete, circular, greyish- 

 white growths which are thickened in the centre, 

 have a thin and often fimbriated or fissured edge, 



