DIPHTHERIA. 137 



of the culture floats on the surface of the liquid, forming a 

 thin whitish pellicle. The bouillon, which is at first cloudy, 

 becomes in a few days clear, and remains so. The sugars con- 

 tained in the bouillon are fermented, and it is due to their 

 fermentation that this medium has at first a tendency to be 

 acid ; but subsequently, when the fermentation is complete, 

 become decidedly more alkaline. On gelatin the colonies 

 develop very slowly. They appear white, round, irregu- 

 larly notched, and somewhat granular, never attaining a large 

 size. On agar the growth presents the same characteristics 

 as on blood-serum ; but on the surface of agar plates the 

 colonies are quite characteristic, having a dark elevated centre 

 and flat periphery, with a radiated appearance and indented 

 edges. On potato the growth is invisible at first ; and at 

 the end of several days a thin whitish veil seems to cover the 

 portion of the potato which has been inoculated. In milk it 

 grows at a temperature as low as 20 C., without any appre- 

 ciable change of the medium. 



Pathogenesis. Diphtheria, along with tetanus, should be 

 classified among the toxic diseases. As a matter of fact, the 

 symptoms met with in cases of diphtheria are due to the 

 effects of the toxins secreted by the bacilli; very few, if any, 

 of the microorganisms are ever found in the blood or deep- 

 seated organs in cases of this disease ; and filtered cultures from 

 which the bacilli have been completely eliminated, when inocu- 

 lated into animals give rise to symptoms identical with those 

 induced by inoculation of the virulent bacilli themselves. 

 Roux and Yersin, by the filtration of cultures through un- 

 glazed porcelain, have been able to separate from the bacilli 

 a toxalbumin which, when injected under the skin of rabbits 

 and guinea-pigs, produces the blood-poisoning, renal and 

 nervous symptoms met with in pure diphtheria. Welch and 

 Abbott have repeated these experiments, and having estab- 

 lished the same facts have come to the same conclusion as to 

 the action of this toxalbumin. 



Subcutaneous inoculations of the diphtheria bacilli will pro- 

 duce death in guinea-pigs in about thirty-six hours. The fol- 

 lowing lesions are found at the autopsy : General oedema at 



