1890.] MICROSCOPICAL JOURJ^AL. 136 



The Condition of Vjiriation. 



By F. HLANCHARD, M. D., 



WASHINGTON, D. C. 



It is the purpose of this article to note some conditions under which 

 species show \ariatiim. with ])articular reference to pathogenic micro- 

 organisms. 



With all our recent advancement, our knowledge of pathogenic mi- 

 crobes is still rudimentary. 



It is unwise to make positi\e assertions concerning them or their 

 functions, to say more than, it is possible, or it is probable. 



Let us then go no farther than to say that, in view of certain familiar 

 facts, it is probable that pathogenic microbes do undergo such changes 

 on account of change of environment, that, if the altered conditions 

 were continued for an indefinite period, the change might amount to 

 specific variation. 



But note well the contlition of change, a change of environment. 

 The advocates of the perpetuity of species too often tbrget this prime 

 condilioo of variation. 



There seems to be no reason why a given species, identical condi- 

 tions being present, mav not continue its characteristic features for 

 ages. The micro-organism of vaccinia is often cited as an example of 

 such persistence. But why has not its character changed ? Simply 

 because its environment has not changed. Every precaution has been 

 taken to prevent a change. Its culture medium has been the living 

 blood of heifers and men. It seems safe to predict that when exper- 

 imenters, who, stimulated by adequate prizes, are now trying to find a 

 safe culture medium for the vaccine virus outside of living bodies, 

 when they have ransacked all possible culture media, they, will be able 

 to show a wide degree of variation in the hitherto imvar\ ing vaccine 

 virus. 



Several observations upon other microbes, noted in the present num- 

 ber of this periodical, render this statement justifiable. L^he piimal 

 requisite of all \ariation is change of environment ; and in this case no 

 change of environment has ever been attempted until now. 



Experimenters have found it very difficult to induce a true diph- 

 theria in the lower animals by introducing into their blood cultures of 

 the supposed diphtheritic germ. 



The poisoned animal dies, but rarely is a pseudo-membrane devel- 

 oped on its mucous surfaces. 



I^he change of medium has produced a modification in the manifes- 

 tation of the germ's pathogenic power. 



It is probable that many prominent symptoms of a given disease are 

 produced, not directly by the presence of myriads of its particular 

 microbe, but by a ptomaine or leucomaine, a by-product of microbic 

 growth. It seems almost certain that the relative amount of this by- 

 product must vary greatly in difierent epidemics of the same disease. 

 P21se why the variation in the intensity of the svmptoms? In one epi- 

 tlemic of scarlatina the symptoms are so mild that the little patients 

 seem hardly sick at all. In another epidemic there is such rapid evolu- 

 tion of some toxic agent that rugged children die before the character- 

 istic eruption appeals. 



