THE DIPHTHERIA BACILLUS 117 



effect upon its virulence, since the organism has been 

 proved to be virulent after four and eight months in the 

 ear and nose. 



The guinea-pig, rabbit, dog, cat, horse, and cow, are 

 all susceptible to infection with the diphtheria bacillus. 

 Rats and mice are refractory. A disease of cats appears 

 to be identical with human diphtheria. They may also 

 harbour diphtheria bacilli without symptoms of the dis- 

 ease. 



Although both are susceptible to infection with the 

 Klebs-Lo filer bacillus, the diseases known respectively 

 as diphtheria of poultry and calves (p. 121) are of a different 

 nature, and non-communicable to man. 



Mixed Infections. In the false membrane the Klebs- 

 Loffler bacillus is often associated with such organisms as 

 Streptococcus pyogenes, staphylococci, and pneumococci. 

 In such cases a high .temperature and foatid throat may 

 be expected, and probably the pathologic process is more 

 serious. W. J. Wilson says that staphylococci may be 

 antagonistic to diphtheria bacilli. 



Diphtheria Toxin and Antitoxin. The nature of the 

 extracellular toxin is not known, but it probably consists 

 of protein. When injected into an animal in doses, 

 sublethal at first and gradually increasing, an antitoxin 

 is formed. 



In addition to the toxin, a diphtheria broth culture 

 contains other substances called toxones and toxoids that 

 combine with antitoxin. Toxoids are non-toxic deriva- 

 tives of toxin. Toxones are primary secretory bodies 

 that produce induration, necrosis, and paralysis. 



Preparation of the Toxin. A virulent culture (grown 

 in slightly alkaline beef broth at 37 C., with free access 

 of air, for a week) is filtered through a Pasteur-Chamber- 

 land filter. The toxicity of the filtrate should be such that 

 not more than O'Ol c.c. will kill a 250-gramme guinea- 

 pig in forty-eight hours. 



Immunisation of the Horse. A small dose of toxin is 

 injected into the withers, together with a dose of anti- 

 toxin. A slight swelling appears, and after a few days 

 subsides, when the operation is repeated, using a larger 

 quantity of toxin. A swelling again appears; when this 

 has in turn subsided, further injections are made, till 

 it is possible to inject 500 c.c. of toxin without injury 



