-the sort of criticism
with which biologists and biological teachings are visited. I am told
every now and then that there is a "brilliant article"[5] in so-and-so,
in which we are all demolished. I used to read these things once, but I
am getting old now, and I have ceased to attend very much to this cry of
"wolf." When one does read any of these productions, what one finds
generally, on the face of it, is that the brilliant critic is devoid of
even the elements of biological knowledge, and that his brilliancy is
like the light given out by the crackling of thorns under a pot of which
Solomon speaks. So far as I recollect, Solomon makes use of the image
for purposes of comparison; but I will not proceed further into that
matter.

Two things must be obvious: in the first place, that every man who has
the interests of truth at heart must earnestly desire that every
well-founded and just criticism that can be made should be made; but
that, in the second place, it is essential to anybody's being able to
benefit by criticism, that the critic should know what he is talking
about, and be in a position to form a mental image of the facts
symbolised by the words he uses. If not, it is as obvious in the case of
a biological argument, as it is in that of a historical or philological
discussion, that such criticism is a mere waste of time on the part of
its author, and wholly undeserving of attention on the part of those who
are criticised. Take it then as an illustration of the importance of
biological study, that thereby alone are men able to form something like
a rational conception of what constitutes valuable criticism of the
teachings of biologists.[6]

Next, I may mention another bearing of biological knowledge--a more
practical one in the ordinary sense of the word. Consider the theory of
infectious disease. Surely that is of interest to all of us. Now the
theory of infectious disease is rapidly being elucidated by biological
study. It is possible to produce, from among the lower animals, examples
of devastating diseases which spread in the same manner as our
infectious disorders, and which are certainly and unmistakably caused by
living organisms. This fact renders it possible, at any rate, that that
doctrine of the causation of infectious disease which is known under the
name of "the germ theory" may be well-founded; and, if so, it must needs
lead to the most important practical measures in dealing with those
terrible