438 FRAGMENTS OF SCIENCE 



of growth; and had they to speak of the subject to-day 

 they would be able to announce an enormous strengthen- 

 ing of the theoretic fibre. Fissures in continuity which 

 then existed, and which left little hope of being ever 

 spanned, have been since filled in, so that the further 

 the theory is tested the more fully does it harmonize 

 with progressive experience and discovery. We shall 

 probably never fill all the gaps; but this will not pre- 

 vent 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 as- 

 sumes 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 prob- 

 ability 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 Yirchow toward that theory. "I must beg my 

 friend Klebs to pardon me," he says, "if, notwithstand- 

 ing the late advances made by the doctrine of infectious 

 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 Yirchow, 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 



