230 
SCIENCE. 
the contrary, the unions which these affinities by themselves 
produce can only be reached through the dissolution and 
destruction of living bodies. The subjugation of chemical 
forces under some higher form of energy, which works 
them for the continued maintenance of a separate individu- 
ality — this is of the very essence of Life. The destruction 
of that separateness is of the very essence of death. It is 
not Life, but the cessation of Life, which, in this sense and 
after this manner, effects a chemical union of the elements 
of the body with the elements around it. There is indeed 
an adjustment — a close, an intricate adjustment — between 
these and the living body ; but it is an adjustment of them 
under the controlling energy of a power which cannot be 
identified with any other, and which always presents pheno- 
mena peculiar to itself. Under that power we see that the 
laws and forces of chemical affinity, as exhibited apart from 
Life, are held, as it were, to service — compelled, indeed, to 
minister but not allowed to rule. Through an infinite 
variety of organisms, this mysterious subordination is main- 
tained, ministering through an ascending series to higher 
and higher grades of sensation, perception, consciousness, 
and thought. 
And here we come in sight of the highest adjustment of all. 
Sensation, perception, consciousness, and thought — these, if 
they be not the very essence of Life, are at least — in their 
order — its highest accompaniments and result. They are the 
ultimate facts, they are the final realities, to which all lesser 
adjustments are themselves adjusted. For, as the elemen- 
tary substances and the elementary forces of Nature which 
are used in the building of the body are there held by the 
energies of Life under a special and peculiar relation to those 
same elements and to those same forces outside the body, 
so also are they held in peculiar relations to those character- 
istic powers in which we are compelled to recognize the rudi- 
mentary faculties of mind, Sensation is the first of these, 
and if it be the lowest, it is at least the indispensable basis 
of all the rest. As such, it cannot be studied too attentively 
in the first stages of its appearance, if we desire to under- 
stand the unity of which it is the index and result. We 
have seen that the mechanism of living bodies is one 
throughout the whole range of animal Life — one in its gen- 
eral plan, and one even in the arrangement of many of its 
details. We have seen, too, that this unity rests upon that 
other — in virtue of which all organisms depend for the 
maintenance of their life, upon adjustments to certain 
physical laws which are held, as it were, in vassalage, and 
compelled to service ; doing in that service what they never 
do alone, and not doing in that service what they always do 
when freed from it. 
And now we have to ask what that service is? We can 
only say that it is the service of Life in all its manifestations, 
from those which we see in the lowest creatures up to the 
highest of which, in addition, we are conscious in ourselves. 
I say “ in addition ” — because this is the fundamental les- 
son of physiology and of comparative anatomy — that the 
principle and the mechanism of sensation are the same in 
all creatures, at least in all which have the rudiments of a 
nervous system. This identity of principle and of struc- 
ture in the machinery of sensation, taken together with the 
identity of the outward manifestations which accompany 
and indicate its presence in animals, makes it certain that 
in itself it is everywhere the same. This does not mean, of 
course — very far from it — that the range of pleasure or of 
pain consequent on sensation — still less the range of intel- 
ligent perception — is the same throughout the animal king- 
dom. The range of pleasure or of pain, and still more the 
range of intelligent perception, depends on the association 
of higher faculties with mere sensation, and upon other 
peculiarities or conditions of organization. We all know 
by our own experience, when comparing ourselves with 
ourselves in different states of health or of disease, and by 
observing the like facts in others, that the degree of pleas- 
ure or of suffering, of emotion or of intellectual activity, 
which is connected with sensation, may be almost infinitely 
various according to various conditions of the body. But 
this does not affect the general proposition that sensation is 
in itself one thing throughout the animal kingdom. It 
cannot be defined in language, because all language is 
founded on it, assumes it to be known, and uses the meta- 
phors it supplies for the expression of our highest intellec- 
tual conceptions. But though it cannot be defined, this at 
least we can say concerning it, that sensation is the charac- 
teristic property of animal life ; that it is an affection of the 
“ amma,” of that which distinguishes animate from inani- 
mate things, and that as such it constitutes one of the most 
essential of the fundamental properties of mind. So true 
is this, that the very word “ idea,” which has played a me- 
morable part in the history of speculation, and which in 
common speech has now come to be generally associated 
with the highest intellectual abstractions, has had in modern 
philosophy no other definite meaning than the impressions 
or mental images received through the senses. This is the 
meaning attached to it (although, perhaps, no writer has 
ever adhered to it with perfect consistency) in the writings 
of Descartes, of Locke, and of Bishop Berkeley ; and it is 
well worthy of remark that the most extreme doctrine of 
Idealism, which denies the reality of matter, and, indeed, 
the reality of everything except mind, is a doctrine which 
may be as logically founded upon sensation in a Zoophyte 
as upon sensation in a Man. The famous proposition of 
Bishop Berkeley, which he considers as almost self-evi- 
dently true, “that the various sensations, or ideas imprinted 
on the sense, cannot exist otherwise than in the mind per- 
ceiving them,” is a proposition clearly applicable to all 
forms of sensation whatever. For every sensation of an 
organism is equally in the nature of an “ idea” in being an 
affection of the living principle, which alone is susceptible 
of such affections ; and it is plainly impossible to conceive 
any sense-impression whatever as existing outside a living 
and perceiving creature. 
We are now, indeed, so accustomed to attach the word 
“ idea ” to the highest exercises of mind, and to confine the 
word “mind” itself to some of its higher manifestations, 
that it may startle some men to be told that sensation is in 
itself a mental affection. We have, however, only to con- 
sider for a moment how inseparably connected sensation is 
with appetite and with perception, to be convinced that in 
the phenomena of sensation we have the first raw materials 
and the first small beginnings of Intelligence and of Will. It 
is this fundamental character of sensation which explains and 
justifies the assertion of philosophers — an assertion which at 
first sight appears to be a mere paradox — that the “ ideas " 
we receive through th : senses have no “ likeness ” to the ob- 
jects they represent. For that assertion, after all, means noth- 
ing more than this — that the impressions made by external 
things upon living beings through the senses, are in them- 
selves mental impressions, and as such cannot be conceived 
as like in their own nature to inanimate and external ob- 
jects. It is the mental quality of all sensation, considered 
in itself, which is really affirmed in this denial of likeness 
between the affections of sense and the things which pro- 
duce those affections in us. It is one of the many forms in 
which we are compelled to recognize the inconceivableness 
of any sort of resemblahce between Mind and Matter, be- 
tween external things and our own perceptive powers. 
And yet it is across this great gulf of difference — appa- 
rently so broad and so profound — that the highest unity of 
Nature is nevertheless established. Matter built up and 
woven into “organs” under the powers of Life is the strong 
foundation on which this unity is established. It is the 
unity which exists between the living organism and the ele- 
ments around it which renders that organism the appro- 
priate channel of mental communication with the external 
world, and a faithful interpreter of its signs. And this the 
organism is — not only by virtue of its substance and com- 
position, but also ana especially by virtue of its adjusted 
structures. All the organs of sense discharge their func- 
tions in virtue of a purely mechanical adjustment between 
the structure of the organ and the particular form of exter- 
nal force which it is intended to receive and to transmit, 
How fine those adjustments are can best be understood 
when we remember that the retina of the eye is a machine 
which measures and distinguishes between vibrations which 
are now known to differ from each other by only a few mil- 
lionths of an inch. Yet this amount af difference is re- 
corded and made instantly appreciable in the sensations of 
color by the adjusted mechanism of the eye. Another ad- 
justment, precisely the same in principle, between the vi- 
brations of Sound and the structure of the ear, enables 
those vibrations to be similarly distinguished in another 
