392 PATHOGENIC BACTERIA. 



The true diphtheria bacilli appear brown with a dark-blue 

 body at one or both ends ; the pseudo-diphtheria bacilli 

 usually exhibit no polar bodies. 



Park ' in his large experience found that neither the 

 Neisser nor the Roux stains gave any more information 

 concerning the virulence of the bacilli than the Loffler 

 alkaline-methylene-blue. 



When cover-glass preparations are stained with these 

 solutions, the bizarre forms already mentioned are much 

 more obvious than in the unstained individuals, and 

 the contrast between the polar granules, which color in- 

 tensely, and the remainder of the bacillus, which tinges 

 slightly, is marked. Through good lenses the organisms 

 are always distinct bacilli, notwithstanding the fact that 

 the ends stain more deeply than the centres, and it is 

 only through poor lenses that the organisms can be mis- 

 taken for diplococci. The bacilli stain well by Gram's 

 method, this being a good method to employ for their 

 definition in sections of tissue, though Welch and Abbott 

 assert that Weigert's fibrin method and picro-carmin give 

 the most beautiful results. 



The diphtheria bacillus does not form spores, and is 

 delicate in its thermal range. Loffler found that it could 

 not endure a temperature. of 6o° C, and Abbott has shown 

 that a temperature of 58 C. for ten minutes is fatal to it. 

 Notwithstanding this susceptibility, the organism can 

 be kept alive for several weeks after being dried upon 

 shreds of silk or when surrounded by dried diphtheria 

 membrane. 



No flagella have been demonstrated upon the bacillus. 

 It is non-motile. 



Fernbach thinks that when the organisms are grown 

 in a medium exposed to a passing current of air, the lux- 

 uriance of their development is increased, though their 

 life-cycle is shorter. The growth can also take place 

 when the air is excluded, so that the bacillus must be 

 classed among the optional anaerobic organisms. 



1 Bacteriology in Medicine and Surgery, 1900. 



