PROFESSOR VIRCHOW AND EVOLUTION. 417 



experience and discovery. We shall probably never fill 

 all the gaps; but this will not prevent a profound belief 

 in the truth of the theory from taking root in the 

 general mind. Much less will it justify a total denial 

 of the theory. The man of science who assumes in 

 such a case the position of a denier is sure to be stranded 

 and isolated. The proper attitude, in my opinion, is to 

 give to the theory during the phases of its growth as 

 nearly as possible a proportionate assent; and, if it be a 

 theory which influences practice, our wisdom is to follow 

 its probable suggestions where more than probability is 

 for the moment unattainable. I write thus with the 

 theory of contagium vivum more especially in my mind, 

 and must regret the attitude of denial assumed by 

 Professor Virchow towards that theory. ' I must beg 

 my friend Klebs to pardon me,' he says, ' if, notwith- 

 standing the late advances made by the doctrine of in- 

 fectious fungi, I still persist in my reserve so far as 

 to admit only the fungus which is really proved, while I 

 deny all other fungi so long as they are not actually 

 brought before me/ Professor Virchow, that is to say, 

 will continue to deny the Germ Theory, however great 

 the probabilities on its side, however numerous be the 

 cases of which it renders a just account, until it has 

 ceased to be a theory at all, and has become a congeries 

 of sensible facts. Had he said, ' As long as a single 

 fungus of disease remains to be discovered, it is your 

 bounden duty to search for it/ I should cordially agree 

 with him. But by his unreserved denial he quenches 

 the light of probability which ought to guide the prac- 

 tice of the medical man. Both here and in relation to 

 the theory of evolution excess upon one side has be- 

 gotten excess upon the other. 



