CH. VI] VARIATIONS IN VIRULENCE 89 



which develops into a virulent parasite, invading the living 

 tissues, undergoes a twofold adaptation, for it must neces- 

 sarily acquire the faculty of nourishing itself upon unac- 

 customed food-stuffs as well as the faculty of excreting toxins. 

 The second would be useless without the first. 



What is the relation between these two faculties? Both 

 imply altered metabolism ; one involves a change in assimi- 

 lation, the other a change in excretion ; one necessitates the 

 assimilation of highly organised materials, in the shape of 

 proteid or extractives, the other consists in the excretion of 

 complex substances which in some cases have been proved to 

 be proteid in nature — the toxalbumins — and in others are 

 more akin to extractives. 



The possibility naturally suggests itself that the second 

 phenomenon may be dependent upon the first, that, in some 

 cases at least, the excretion of toxins is the direct resvlt of the 

 altered assimilation, comparable to the increased toxicity of 

 the urine of a man on a certain diet. 



This hypothesis would go far towards explaining the 

 development of toxicity by saprophytic organisms growing 

 in material of a highly albuminous nature and rich in extrac- 

 tives, in an inflamed uterus or in pathological exudations 

 wherever found, without any actual invasion of the living 

 tissues by the organism taking place. 



Two observations are of interest in this connection. 



(a) Miss Peckham (1897), in speaking of coliform organ- 

 isms, expresses the opinion that the carbohydrate con- 

 stituents of the culture medium are always attacked by the 

 organisms present in preference to the proteid material and 

 it is only when the supply of carbohydrate is exhausted that 

 the proteid is made use of She showed that if B. typhosus 

 were repeatedly subcultured in peptone solution which con- 

 tained no ca/rhohydrate it acquired the power to split up the 

 proteid and produced indol. She also quotes P^r^ to the 

 effect that the appearance of the indol reaction (which 

 depends upon the breaking up of the proteid by the organisms) 

 is proof of the absence of carbohydrate, an opinion she herself 

 confirmed by experiment. She found that indol formation 



