6GO FRAGMENTS OF SCIENCE. 
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 toward 
that theory. " I must beg my friend Klebs to pardon 
me," he says, " if, notwithstanding 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 Virchow, 
that is to say, will continue to deny the germ theory, 
however great the probabilities on its side, however numer- 
ous 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 bouuden 
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 practice of the 
medical man. Both here and in relation to the theory of 
evolution excess upon one side has begotten excess upon 
the other. 
CHAPTER XXXVIII. 
THE ELECTRIC LIGHT.* 
THE SUBJECT of this evening's discourse was proposed by 
our late honorary secretary.! That word "late" has for 
me its own connotations. It implies, among other things, 
the loss of a comrade by whose side I have worked for 
thirteen years. On the other hand, regret is not without 
its opposite in the feeling with which I have seen him rise by 
sheer intrinsic merit, moral and intellectual, to the high- 
est official position which it is in the power of English 
science to bestow. Well, he, whose constant desire and 
* A discourse delivered at the Royal Institution of Great Britain on 
Friday, January 17, 1879, and introduced here as the latest Frag- 
ment. 
f Mr. William Spottis woode, late president of the Royal Society. 
