DIPHTHERIA. 215 



In agar streak-cultures large, grayish-white colonies form, 

 that soon give rise to extensive elevated deposits ; whereas, 

 in the case of the diphtheria-bacillus, development extends 

 only a short distance from the line of inoculation. On 

 serum the colonies soon become larger, brighter, and softer 

 than those of the diphtheria-bacillus. In bouillon they 

 form a precipitate, clarification taking place after the lapse 

 of three weeks. Upon alkaline potato slight growth takes 

 place, and in milk and egg a good growth. Milk is not 

 coagulated. The xerosis-bacilli develop but slightly upon 

 all culture-media. 



The pseudo-diphtheria-bacilli usually generate no acid in 

 their development in ordinary bouillon ; individual varieties 

 form minimal amounts, and only one culture of xerosis- 

 bacilli is mentioned by Neisser that exhibited as great an 

 increase in acidity as is observed in the case of diphtheria- 

 bacilli. 



On the whole, the pseudo-diphtheria-bacilli and the 

 xerosis-bacilli are not pathogenic for guinea-pigs, although, 

 according to Spronck and C. Frankel, there are some 

 varieties that exhibit a certain degree of virulence for these 

 animals (causing edema, and after inoculation of three cubic 

 centimeters loss of weight, etc.). The guinea-pigs could 

 not be protected against the action of these pseudo-bacilli 

 by previous injection of diphtheria-antitoxin. The observ- 

 ers named, therefore, reached the conclusion that diphtheria- 

 bacilli and pseudo-diphtheria-bacilli are not identical. Roux 

 and Yersin, however, take the position that the pseudo- 

 diphtheria-bacillus represents an attenuated or temporarily 

 nonvirulent diphtheria-bacillus. This view still has ad- 

 herents, who support their contention with the fact that in 

 every case of true severe diphtheria nonvirulent as well as 

 virulent diphtheria-bacilli are always observed. The diph- 

 theria-bacillus would, accordingly, be somewhat analogous 

 to the pneumococcus, which, likewise, is a common inhabi- 

 tant of the healthy mouth. 



The Susceptibility of Human Beings to Diphtheria 

 can not be considered as great, in view of the possibility 

 of the presence of diphtheria-bacilli upon the mucous mem- 

 brane of healthy persons. It would appear that a special 

 predisposition on the part of the mucous membranes or 

 special virulence on the part of the bacilli is necessary for 

 the development of the disease. The first years of life have 



