especially exhibited by a
nitrogenous contractile substance, which in plants is limited
and fettered by an inert membrane, in animals not so."[1]

[Footnote 1: Cohn, "Ueber Protococcus pluvialis," in the "Nova Acta"
for 1850.]

In 1868, thinking that an untechnical statement of the views current
among the leaders of biological science might be interesting to the
general public, I gave a lecture embodying them in Edinburgh. Those
who have not made the mistake of attempting to approach biology,
either by the high _a priori_ road of mere philosophical speculation,
or by the mere low _a posteriori_ lane offered by the tube of a
microscope, but have taken the trouble to become acquainted with
well-ascertained facts and with their history, will not need to be
told that in what I had to say "as regards protoplasm" in my lecture
"On the Physical Basis of Life," there was nothing new; and, as I
hope, nothing that the present state of knowledge does not justify us
in believing to be true. Under these circumstances, my surprise may be
imagined, when I found, that the mere statement of facts and of views,
long familiar to me as part of the common scientific property of
continental workers, raised a sort of storm in this country, not only
by exciting the wrath of unscientific persons whose pet prejudices
they seemed to touch, but by giving rise to quite superfluous
explosions on the part of some who should have been better informed.

Dr. Stirling, for example, made my essay the subject of a special
critical lecture[1], which I have read with much interest, though, I
confess, the meaning of much of it remains as dark to me as does the
"Secret of Hegel" after Dr. Stirling's elaborate revelation of it.
Dr. Stirling's method of dealing with the subject is peculiar.
"Protoplasm" is a question of history, so far as it is a name; of
fact, so far as it is a thing. Dr. Stirling has not taken the trouble
to refer to the original authorities for his history, which is
consequently a travesty; and still less has he concerned himself with
looking at the facts, but contents himself with taking them also at
secondhand. A most amusing example of this fashion of dealing with
scientific statements is furnished by Dr. Stirling's remarks upon my
account of the protoplasm of the nettle hair. That account was drawn
up from careful and often-repeated observation of the facts. Dr.
Stirling thinks he is offering a valid criticism, when he says tha