SCIENCE. 
229 
faculty of appropriating foreign substances into its own, 
making them subservient to the renewal of its own material, 
to the maintenance of its own energy, and to the preserva- 
tion of its own separate individuality. It has the faculty, 
moreover, of giving off parts of itself, endowed with the 
same properties, to lead a separate existence. This same 
substance, which when analyzed has always the same 
chemical composition, and when alive has always the same 
fundamental properties, is at the root of every organism, 
whether animal or vegetable. Out of its material all visible 
structure is 1 uilt up, and the power which holds its ele- 
ments together is the same power which performs the 
further work of molding them into tissues — first forming 
them, and then feeding them, and then keeping them in 
life. This is as true of the highest organism of Man as it is 
of the lowest, in which visible structure begins to be. The 
phenomena of disease have convinced physiologists that all 
the tissues of the body are freely penetrated by the proto- 
plasmic corpuscles of the blood, and that the primordial 
properties displayed in the substance of an Amoeba, which 
has no distinguishable parts and no separate organs, afford 
the only key to the fundamental properties of every animal 
body. One eminent observer assigns so high a place to 
this protoplasmic matter as the primary physical agent in 
the building of the House of Life, and in its renovation 
and repair, that he considers all its other materials, and all 
its completed structures as comparatively “ dead.” 
But the unity of Man’s body with the rest of Nature lies 
deeper still than this. The same elements and the same 
primary compounds are but the foundations from which the 
higher unities arise. These higher unities appear to depend 
upon and to be explained by this — that there are certain 
things which must be done for the support of animal life, 
and these things are fundamentally the same from the low- 
est to the highest creatures. It is for the doing of these 
things that “organs” are required, and it is in response to 
this requirement that they are provided. Food — that is to 
say, foreign material — must be taken in, and it must be as- 
similated. The circulating fluids of the body must absorb 
oxygen ; and when this cannot be done more simply, a 
special apparatus must be provided for the separation of 
this essential element of life from the air or from the water. 
Sensation must be localized and adapted to the perception 
of movements in surrounding media. The tremors of the 
atmosphere and of the luminiferous ether must first be 
caught upon responsive — that is to say, upon adapted — 
surfaces, and then they must be translated into the language 
of sensation — that is to say, into sight and hearing. The heat 
evolved in the chemical processes of digestion and of oxygen- 
ation of the blood must be made convertible into other forms 
of motion. The forces thus concentrated must be stored, 
rendered accessible to the Will, and distributed to members 
which are at its command. These and and many other 
uniform necessities of the animal frame constitute a unity 
of function in organs of the widest dissimilarity of form, so 
that however different they may be in shape, or in structure, 
or in position, they are all obviously reducible to one com- 
mon interpretation. They do the same things — they serve 
the same purposes — they secure the same ends — or, to use 
the language of physiology, they discharge the same func- 
tions in the animal economy. 
But more than this ; even the differences of form steadily 
diminish as we ascend in the scale of being. Not only are 
the same functions discharged, but they are discharged by 
organs of the same general shape, formed on one pattern, 
and occupying an identical position in one plan of structure. 
It is on this fact that this science of comparative anatomy 
is founded, and the well-established doctrine of “homolo- 
gies.” The homology of two organs in two separate animals 
is nothing but the unity of place which they occupy in a 
structure which is recognized as one and the same in a vast 
variety of creatures — a structure which is one in its general 
conception, and one in the relative arrangement of its 
parts. In this clear and very definite sense, the body of 
Man, as a whole, is one in structure with the bodies of all 
vertebrate animals ; and as we rise from the lowest of these 
to him who is the highest, we see that same structure ela- 
borated into closer and closer likeness, until every part 
corresponds — bone to bone, tissue to tissue, organ to organ. 
It is round this fact that so many disputants are now fight- 
ing. But all the controversy arises, not as to the existence 
of the fact, but as to its physical cause. The fact is beyond 
question. In a former work 2 I have dwelt at some length 
on the bearing of this fact on our conceptions of “ Creation 
by Law,” and on the various theories which assume that 
such close relationship in organic structure can be due to 
no other cause than blood relationship through ordinary 
generation. At present I am only concerned with the fact 
of unity, whatever may be the physical cause from which 
that unity has arisen. The significance of it, as establishing 
Man’s place in the unity of Nature, is altogether independ- 
ent of any conclusion which may be reached as to those 
processes of creation by which his body has been fashioned 
on a plan which is common to him and to so many animals 
beneath him. Whether Man has been separately created 
out of the inorganic elements of which his body is com- 
posed, or whether it was born of matter previously organ- 
ized in lower forms, this community of structure must 
equally indicate a corresponding community of relations 
with external things, and some antecedent necessity deeply 
seated in the very nature of tliose things, why his bodily 
frame should be like to theirs. 
And, indeed, when we consider the matter, it is sufficiently 
apparent that the relationship of Man’s body to the bodies of 
the lower animals is only a subordinate part and consequence 
of that higher and more general relationship which prevails 
between all living things and those elementary forces of 
Nature which play in them, and around them, and upon 
them. If we could only know what that relationship is in 
its real nature and in its full extent, we should know one ol 
the most inscrutable of all secrets. For that secret is no 
other than the ultimate nature of Life. The great matter is 
to keep the little knowledge of it which we possess safe from 
the confusing effect of deceptive definitions. The real uni- 
ties of Nature will never be reached by confounding her 
distinctions. For certain purposes it may be a legitimate 
attempt to reduce the definition of Life to its lowest terms — 
that is to say, it may be legitimate to fix our attention ex- 
clusively on those characteristics which are common to Life 
in its lowest and in its highest forms, and to set aside all 
other characteristics in which they differ. It may be useful 
sometimes to look at Life under the terms of such a defini- 
tion, in order, for example, the better to conceive some of 
its relations with other things. But in doing so we must 
take care not to drop out of the terms so defining Life any- 
thing really essential to the very idea of it. Artificial defini- 
tions of this kind are dangerous experiments in philosophy. 
It is very easy by mere artifices of language to obliterate the 
most absolute distinctions which exist in Nature. Between 
the living and the non-living there is a great gulf fixed, and 
the indissoluble connection which somehow, nevertheless, 
we know to exist between them is a connection which does 
not fill up that gulf, but is kept up by somebiidge being, as 
it were, artificially built across it. This unity, like the other 
unities of Nature, is not a unity consisting of mere contin- 
uity of substance. It is not founded upon sameness, but, 
on the contrary, rather upon difference, and even upon an- 
tagonisms. Only the forces which are thus different and 
opposed are subordinate to a system of adaptation and ad- 
justment. Nor must we fail to notice the kind of unity 
which is implied in the very words “ adaptation ” and “ ad- 
justment ” — and, above all others, in the special adjustments 
connected with organic Life. There are many unions which 
do not involve the idea of adjustment, or which involve it 
only in the most rudimentary form. The mere chemical 
union of two or more elements — unless under special con- 
ditions — is not properly an adjustment. We should not 
naturally call the formation of rust an adjustment between 
the oxygen of the atmosphere and metallic iron. When 
the combinations , effected by the play of chemical affi- 
nities are brought about by the selection of elements 
so placed within reach of each other’s reactions as to 
result in a given product, then that product would 
be accurately described as the result of co-ordination 
and adjustment. But the kind of co-ordination and 
adjustment which appears in the facts of Life is of a still 
higher and more complicated kind than this. Whatever 
the relationship may be between living organisms and the 
elements, or elementary forces of external Nature, it cer- 
tainly is not the relationship of mere chemical affinities. On 
2 41 The Reign of Law.’* 
