CH. vin] TRANSMUTATION IN THE LIVING BODY 115 



might be thought to represent no less wide a divergence in 

 type, may disappear entirely under certain conditions con- 

 ditions, be it noted, precisely analogous to those which we 

 have surmised might bring about a similar result in the cases 

 we have been considering namely, invasion of the living body. 

 The experiments of Eyre, Leatham and Washbourn (1906) 

 with strains of the pneumococcus furnish an example. These 

 observers describe the virulent, parasitic pneumococcus as re- 

 quiring for its growth a certain reaction and temperature, and 

 particular media (blood agar) ; it would not grow if the reaction 

 were even faintly acid or at a temperature much below 37 C. 

 and rapidly died out on agar or in broth. It would not liquefy 

 gelatin and in broth formed a dust-like deposit. The avirulent 

 saprophytic variety, on the other hand, grew luxuriantly at 

 temperatures ranging from 37 to 20 C. on agar, gelatin, 

 potato or in broth, whether acid or alkaline, slowly liquefying 

 gelatin and producing a uniform turbidity in broth. It retained 

 its vitality for many months. It also exhibited differences in 

 its morphology, " instead of isolated diplococci and strepto- 

 cocci large masses of cocci and diplococci were found and 

 forms dividing into tetrads were common." Nevertheless this 

 avirulent saprophytic pneumococcus could, by a single " pas- 

 sage " through a rabbit, be converted into a typical parasitic 

 pneumococcus of high virulence. 



Such a remarkable transition, if it did not actually happen, 

 would seem to us quite as improbable as a transition from, 

 let us say, the micrococcus catarrhalis to the meningococcus. 



The purpose of this section is to suggest that a change in 

 character, comparable to that brought about in the case of the 

 saprophytic pneumococcus by a single animal passage, might 

 be brought about in the case of other saprophytic organisms 

 by an analogous process, namely by their invasion of the living 

 body when the lowered vitality or the inflamed condition of 

 the tissues enable them to gain a foothold therein. 



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