186 BACTERIOLOGY FOR NURSES 



of diphtheria or in the throats of healthy individuals suspected 

 of being carriers is known save that of animal inoculation. For 

 this purpose an alkaline forty-eight-hour broth culture is employed 

 and two guinea pigs are inoculated subcutaneously, one with two 

 c.c. of the culture, the other with the same amount of culture plus 

 a protective amount of antitoxin. If within four days the guinea 

 pig receiving the toxin only dies, and the one receiving the toxin 

 plus antitoxin lives, the organisms injected were undoubtedly 

 diphtheria bacilli. 



Another and more economical method is as follows : the hair 

 is removed from the abdominal surface of two 250 gram guinea 

 pigs, by shaving or plucking. The twenty-four-hours growth 

 on Loeffler's serum of the organism to be tested is emulsified with 

 20 c.c. of salt solution, and 0.15 c.c. of this suspension is injected 

 intracutaneously into the prepared abdominal surface of each of 

 the two guinea pigs. One of the animals is injected intracardially 

 at the same time with 250 units of antitoxin or an intraperitoneal 

 injection of the antitoxin is made twenty-four hours before. In 

 this way six cultures may be tested on the same animals. Virulent 

 diphtheria bacilli produce an infiltration and superficial necrosis 

 at the site of inoculation in from two to three days, while in 

 the guinea pig protected by the antitoxin the skin remains 

 normal. 



Bacteria Resembling Bacillus Diphtheria. Bacillus Hoff- 

 manni organisms often spoken of as pseudo diphtheria bacilli are 

 frequently found in normal throats and in some instances in those 

 of diphtheritic individuals. At first they were regarded as atten- 

 uated diphtheria bacilli. Later investigators, however, consider 

 them as a different species. They appear as short, thick rods, 

 stain solidly with methylene blue, do not show granules when 

 stained with Neisser's stain, are not motile, and do not form spores. 

 Their colony growth on Loeffler's serum media closely resembles 

 that of the diphtheria bacillus. They differ from the latter or- 

 ganism, however, in that they are unable to ferment any of the 

 sugars; they do not produce toxin and are not pathogenic for 

 guinea pigs. 



