130 ON VARIABILITY AND ADAPTATION 



This form is very rare in malignant cases of diphtheria — it 

 is more abundant in benign, and becomes increasingly common 

 as severe diphtheria progresses towards cure. But, as I have 

 already indicated, it is to be discovered in non-diphtherial cases. 

 At the Hopital des Enfants Malades, Paris, from the pharyn- 

 geal mucous membrane of 45 children not affected with the 

 disease it was obtained in 15 cases, and of 59 healthy school 

 children at Caen, in a school where for long there had been no 

 diphtheria, no less than 26 gave growths of this form, though it 

 must be confessed that the colonies were few and far between. 

 Inoculation into guinea-pigs and rabbits never led to fatal 

 results, and yet differences were observable. Some guinea-pigs 

 manifested a very considerable oedema at the point of inocula- 

 tion, in others a slight oedema was to be seen, others presented 

 no sign of even local disturbance. It is noteworthy that the 

 most marked oedema was developed where cultures were employed 

 whose origin was from cases of measles. 



Oedema at the point of inoculation is one of the character- 

 istic lesions when virulent diphtheria bacilli are injected, and 

 Roux and Yersin found that if they attenuated virulent cultures 

 either by the action of air and high temperature, or, again, if 

 they preserved dried-up false membranes for five months in 

 a cool place and in the dark, they gained colonies, some of which 

 caused no oedema, others a little, one alone caused marked 

 oedema. Such attenuated bacilli, like the Bacillus pseudo- 

 diphthericus, grew more abundantly at a lower temperature, 

 and, like this, also rendered broth more rapidly alkaline. In 

 fact, the only point distinguishing the two was that our observers 

 succeeded in intensifying the virulence of the attenuated form, 

 and failed to do this with the Pseudo-diphtherial bacillus. In 

 every other respect the proof appears conclusive that this Bacillus 

 pseudo-diphthericus is a natural race, or races, of the Bacillus 

 diphthericus, that it is no wise a separate species of independent 

 origin. 



What is more, Roux and Yersin suggest an explanation of 

 the onset of diphtheria — of the natural intensification, that is, 

 of the virus in man. Just as they found that from a case of 

 measles presenting no sign of diphtheria proper they gained a 

 race of the Bacillus pseudo-diphthericus, which exhibited distinct, 

 if slight, virulence, so have they noticed cases in which, through 



