THE BACILLUS AND THE BACTERIOLOGY OF DIPHTHERIA 221 



of the animal inoculated, unless controls with antitoxin are made. 

 In the large majority of cases, when the bacilli are virulent, this amount 

 causes death within seventy-two hours. At the autopsy the character- 

 istic lesions already described are found. Bacilli which in cultures 

 and in animal experiments have shown themselves to be characteristic 

 may be regarded for practical purposes as certainly true diphtheria 

 bacilli, and as capable of producing diphtheria in man under favorable 

 conditions. 



For an absolute test of specific virulence antitoxin must be used. 

 A guinea-pig is injected with antitoxin, and then this and a control 

 animal, with 2 c.c. of a broth culture of the bacilli to be tested, 

 if the guinea-pig which received the antitoxin lives, while the control 

 dies, it was surely a diphtheria bacillus which killed by means of diph- 

 theria toxin or, in other words, not simply a virulent bacillus, but a 

 virulent diphtheria bacillus. When the bacilli to be tested grow poorly 

 in a simple nutrient bouillon they should be grown in bouillon to which 

 one-third its quantity of ascitic fluid has been added. Quite a number 

 of bacilli have been met with which killed 250-grm. guinea-pigs in 

 doses of 2 to 15 c.c., and yet were unaffected by antitoxin. These 

 bacilli, though slightly virulent to guinea-pigs, produce no diphtheria 

 toxin, and so cannot, to the best of our belief, produce diphtheria in 

 man. 



