TRANSCENDENTAL PHYSIOLOGY.

[_First published in_ The National Review _for October,_ 1857_,

under the title of "The Ultimate Laws of Physiology". The title

"Transcendental Physiology", which the editor did not approve, was

restored when the essay was re-published with others in_ 1857.]

The title Transcendental Anatomy is used to distinguish that division of

biological science which treats, not of the structures of individual

organisms considered separately, but of the general principles of

structure common to vast and varied groups of organisms,--the unity of

plan discernible throughout multitudinous species, genera, and orders,

which differ widely in appearance. And here, under the head of

Transcendental Physiology, we purpose putting together sundry laws of

development and function which hold not of particular kinds or classes

of organisms, but of all organisms: laws, some of which have not, we

believe, been hitherto enunciated.

By way of unobtrusively introducing the general reader to biological

truths of this class, let us begin by noticing one or two with which he

is familiar. Take first, the relation between the activity of an organ

and its growth. This is a universal relation. It holds, not only of a

bone, a muscle, a nerve, an organ of sense, a mental faculty; but of

every gland, every viscus, every element of the body. It is seen, not in

man only, but in each animal which affords us adequate opportunity of

tracing it. Always providing that the performance of function is not so

excessive as to produce disorder, or to exceed the repairing powers

either of the system at large or of the particular agencies by which

nutriment is brought to the organ,--always providing this, it is a law

of organized bodies that, other things equal, development varies as

function. On this law are based all maxims and methods of right

education, intellectual, moral, and physical; and when statesmen are

wise enough to see it, this law will be found to underlie all right

legislation.

Another truth co-extensive with the organic world, is that of hereditary

transmission. It is not, as commonly supposed, that hereditary

transmission is exemplified merely in re-appearance of the family

peculiarities displayed by immediate or remote progenitors. Nor does the

law of hereditary transmission comprehend only such more general facts

as that modified plants or animals become the parents of permanent

varieties; and that new kinds of potatoes, new breeds of sheep, new

races of men, have been thus originated. These are but minor

exemplifications of the law. Understood in its entirety, the law is that

each plant or animal produces others of like kind with itself: the

likeness of kind consisting not so much in the repetition of individual

traits as in the assumption of the same general structure. This truth

has been made by daily illustration so familiar as nearly to have lost

its significance. That wheat produces wheat,--that existing oxen are

descended from ancestral oxen,--that every unfolding organism ultimately

takes the form of the class, order, genus, and species from which it

sprang; is a fact which, by force of repetition, has assumed in our

minds the character of a necessity. It is in this, however, that the law

of hereditary transmission is principally displayed; the phenomena

commonly named as exemplifying it being quite subordinate

manifestations. And the law, as thus understood, is universal. Not

forgetting the apparent, but only apparent, exceptions presented by the

strange class of phenomena known as "alternate generation," the truth

that like produces like is common to all types of organisms.

Let us take next a universal physiological law of a less conspicuous

kind. To the ordinary observer, it seems that the multiplication of

organisms proceeds in various ways. He sees that the young of the higher

animals when born resemble their parents; that birds lay eggs, which

they foster and hatch; that fish deposit spawn and leave it. Among

plants, he finds that while in some cases new individuals grow from

seeds only, in other cases they also grow from tubers; that by certain

plants layers are sent out, take root, and develop new individuals; and

that many plants can be reproduced from cuttings. Further, in the mould

that quickly covers stale food, and the infusoria that soon swarm in

water exposed to air and light, he sees a mode of generation which,

seeming inexplicable, he is apt to consider "spontaneous." The reader of

popular science thinks the modes of reproduction still more various. He

learns that whole tribes of creatures multiply by gemmation--by a

development from the body of the parent of buds which, after unfolding

into the parental form, separate and lead independent lives. Concerning

microscopic forms of both animal and vegetal life, he reads that the

ordinary mode of multiplication is by spontaneous fission--a splitting

up of the original individual into two or more individuals, which by and

by severally repeat the process. Still more remarkable are the cases in

which, as in the _Aphis_, an egg gives rise to an imperfect female, from

which other imperfect females are born viviparously, grow, and in their

turns bear other imperfect females; and so on for eight, ten, or more

generations, until finally, perfect males and females are viviparously

produced. But now under all these, and many more, modified modes of

multiplication, the physiologist finds complete uniformity. The

starting-point, not only of every higher animal or plant, but of every

clan of organisms which by fission or gemmation have sprung from a

single organism, is always a spore, seed, or ovum. The millions of

infusoria or of aphides which, by sub-division or gemmation, have

proceeded from one individual; the countless plants which have been

successively propagated from one original plant by cuttings or tubers;

are, in common with the highest creature, primarily descended from a

fertilized germ. And in all cases--in the humblest alga as in the oak,

in the protozoon as in the mammal--this fertilized germ results from the

union of the contents of two cells. Whether, as among the lowest forms

of life, these two cells are seemingly identical in nature; or whether,

as among higher forms, they are distinguishable into sperm-cell and

germ-cell; it remains throughout true that from their combination

results the mass out of which is evolved a new organism or new series of

organisms. That this law is without exception we are not prepared to

say; for in the case of the _Aphis_ certain experiments are thought to

imply that under special conditions the descendants of an original

individual may continue multiplying for ever, without further

fecundation. But we know of no case where it _actually is_ so; for

although there are certain plants of which the seeds have never been

seen, it is more probable that our observations are in fault than that

these plants are exceptions. And until we find undoubted exceptions, the

above-stated induction must stand. Here, then, we have another of the

truths of Transcendental Physiology: a truth which, so far as we know,

_transcends_ all distinctions of genus, order, class, kingdom, and

applies to every living thing.

Yet another generalization of like universality expresses the process of

organic development. To the ordinary observer there seems no unity in

this. No obvious parallelism exists between the unfolding of a plant and

the unfolding of an animal. There is no manifest similarity between the

development of a mammal, which proceeds without break from its first to

its last stage, and that of an insect, which is divided into

strongly-marked stages--egg, larva, pupa, imago. Nevertheless it is now

an established fact, that all organisms are evolved after one general

method. At the outset the germ of every plant or animal is relatively

homogeneous; and advance towards maturity is advance towards greater

heterogeneity. Each organized thing commences as an almost structureless

mass, and reaches its ultimate complexity by the establishment of

distinctions upon distinctions,--by the divergence of tissues from

tissues and organs from organs. Here, then, we have yet another

biological law of transcendent generality.

Having thus recognized the scope of Transcendental Physiology as

presented in its leading truths, we are prepared for the considerations

that are to follow.

* * * * *

And first, returning to the last of the great generalizations above

given, let us inquire more nearly how this change from the homogeneous

to the heterogeneous is carried on. Usually it is said to result from

successive differentiations. This, however, cannot be considered a

complete account of the process. During the evolution of an organism

there occur, not only separations of parts, but coalescences of parts.

There is not only segregation, but aggregation. The heart, at first a

simple pulsating blood-vessel, by and by twists upon itself and becomes

integrated. The bile-cells constituting the rudimentary liver, do not

merely diverge from the surface of the intestine in which they at first

form a simple layer; but they simultaneously consolidate into a definite

organ. And the gradual concentration seen in these and other cases is a

part of the developmental process--a part which, though more or less

recognized by Milne-Edwards and others, does not seem to have been

included as an essential element in it.

This progressive integration, manifest alike when tracing up the several

stages passed through by every embryo, and when ascending from the lower

organic forms to the higher, may be most conveniently studied under

several heads. Let us consider first what may be called _longitudinal

integration_.

The lower _Annulosa_--worms, myriapods, &c.--are characterized by the

great numbers of segments of which they respectively consist, reaching

in some cases to several hundreds; but as we advance to the higher

_Annulosa_--centipedes, crustaceans, insects, spiders,--we find these

numbers greatly reduced, down to twenty-two, thirteen, and even fewer;

and accompanying this there is a shortening or integration of the whole

body, reaching its extreme in crabs and spiders. Similarly with the

development of an individual crustacean or insect. The thorax of a

lobster, which, in the adult, forms, with the head, one compact box

containing the viscera, is made up by the union of a number of segments

which in the embryo were separable. The thirteen distinct divisions seen

in the body of a caterpillar, become further integrated in the

butterfly: several segments are consolidated to form the thorax, and the

abdominal segments are more aggregated than they originally were. The

like truth is seen when we pass to the internal organs. In the lower

annulose forms, and in the larvae of the higher ones, the alimentary

canal consists either of a tube that is uniform from end to end, or else

bulges into a succession of stomachs, one to each segment; but in the

developed forms there is a single well-defined stomach. In the nervous,

vascular, and respiratory systems a parallel concentration may be

traced. Again, in the development of the _Vertebrata_ we have sundry

examples of longitudinal integration. The coalescence of several

segmental groups of bones to form the skull is one instance of it. It is

further illustrated in the _os coccygis_, which results from the fusion

of a number of caudal vertebrae. And in the consolidation of the sacral

vertebrae of a bird it is also well exemplified.

That which we may distinguish as _transverse integration_, is well

illustrated among the _Annulosa_ in the development of the nervous

system. Leaving out those simple forms which do not present distinct

ganglia, it is to be observed that the lower annulose animals, in common

with the larvae of the higher, are severally characterized by a double

chain of ganglia running from end to end of the body; while in the more

advanced annulose animals this double chain becomes a single chain. Mr.

Newport has described the course of this concentration in insects; and

by Rathke it has been traced in crustaceans. In the early stages of the

_Astacus fluviatilis_, or common cray-fish, there is a pair of separate

ganglia to each ring. Of the fourteen pairs belonging to the head and

thorax, the three pairs in advance of the mouth consolidate into one

mass to form the brain, or cephalic ganglion. Meanwhile out of the

remainder, the first six pairs severally unite in the median line, while

the rest remain more or less separate. Of these six double ganglia thus

formed, the anterior four coalesce into one mass; the remaining two

coalesce into another mass; and then these two masses coalesce into one.

Here we see longitudinal and transverse integration going on

simultaneously; and in the highest crustaceans they are both carried

still further. The _Vertebrata_ exhibit this transverse integration in

the development of the generative system. The lowest of the

mammalia--the _Monotremata_--in common with birds, have oviducts which

towards their lower extremities are dilated into cavities severally

performing in an imperfect way the function of a uterus. "In the

_Marsupialia_, there is a closer approximation of the two lateral sets

of organs on the median line; for the oviducts converge towards one

another and meet (without coalescing) on the median line; so that their

uterine dilatations are in contact with each other, forming a true

'double uterus.' ... As we ascend the series of 'placental' mammals, we

find the lateral coalescence becoming gradually more and more

complete.... In many of the _Rodentia_, the uterus still remains

completely divided into two lateral halves; whilst in others, these

coalesce at their lower portion, forming a rudiment of the true 'body'

of the uterus in the Human subject. This part increases at the expense

of the lateral 'cornua' in the higher Herbivora and Carnivora; but even

in the lower Quadrumana, the uterus is somewhat cleft at its

summit."[6] And this process of transverse integration, which is still

more striking when observed in its details, is accompanied by parallel

though less important changes in the opposite sex. Once more; in the

increasing commissural connexion of the cerebral hemispheres, which,

though separate in the lower vertebrata, become gradually more united in

the higher, we have another instance. And further ones of a different

order, but of like general implication, are supplied by the vascular

system.

Now it seems to us that the various kinds of integration here

exemplified, which are commonly set down as so many independent

phenomena, ought to be generalized, and included in the formula

describing the process of development. The fact that in an adult crab,

many pairs of ganglia originally separate have become fused into a

single mass, is a fact only second in significance to the

differentiation of its alimentary canal into stomach and intestine. That

in the higher _Annulosa_, a single heart replaces the string of

rudimentary hearts constituting the dorsal blood-vessel in the lower

_Annulosa_, (reaching in one species to the number of one hundred and

sixty), is a truth as much needing to be comprised in the history of

evolution, as is the formation of a respiratory surface by a branched

expansion of the skin. A right conception of the genesis of a vertebral

column, includes not only the differentiations from which result the

_chorda dorsalis_ and the vertebral segments imbedded in it; but quite

as much it includes the coalescence of numerous vertebral processes with

their respective vertebral bodies. The changes in virtue of which

several things become one, demand recognition equally with those in

virtue of which one thing becomes several. Evidently, then, the current

statement which ascribes the developmental progress to differentiations

alone, is incomplete. Adequately to express the facts, we must say

that the transition from the homogeneous to the heterogeneous is carried

on by differentiations and accompanying integrations.

It may not be amiss here to ask--What is the meaning of these

integrations? The evidence seems to show that they are in some way

dependent on community of function. The eight segments which coalesce to

make the head of a centipede, jointly protect the cephalic ganglion, and

afford a solid fulcrum for the jaws, &c. The many bones which unite to

form a vertebral skull have like uses. In the consolidation of the

several pieces which constitute a mammalian pelvis, and in the

anchylosis of from ten to nineteen vertebrae in the sacrum of a bird, we

have kindred instances of the integration of parts which transfer the

weight of the body to the legs. The more or less extensive fusion of the

tibia with the fibula and the radius with the ulna in the ungulated

mammals, whose habits require only partial rotations of the limbs, is a

fact of like meaning. And all the instances lately given--the

concentration of ganglia, the replacement of many pulsating blood-sacs

by fewer and finally by one, the fusion of two uteri into a single

uterus--have the same implication. Whether, as in some cases, the

integration is merely a consequence of the growth which eventually

brings into contact adjacent parts performing similar duties; or

whether, as in other cases, there is an actual approximation of these

parts before their union; or whether, as in yet other cases, the

integration is of that indirect kind which arises when, out of a number

of like organs, one, or a group, discharges an ever-increasing share of

the common function, and so grows while the rest dwindle and

disappear;--the general fact remains the same, that there is a tendency

to the unification of parts having similar duties.

The tendency, however, acts under limiting conditions; and recognition

of them will explain some apparent exceptions. In the human foetus, as

in the lower vertebrata, the eyes are placed one on each side of the

head. During evolution they become relatively nearer, and at birth are

in front; though they are still, in the European infant as in the adult

Mongol, proportionately further apart than they afterwards become. But

this approximation shows no signs of further increase. Two reasons

suggest themselves. One is that the two eyes have not quite the same

function, since they are directed to slightly-different aspects of each

object looked at; and, since the resulting binocular vision has an

advantage over monocular vision, there results a check upon further

approach towards identity of function and unity of structure. The other

reason is that the interposed structures do not admit of any nearer

approach. For the orbits of the eyes to be brought closer together,

would imply a decrease in the olfactory chambers; and as these are

probably not larger than is demanded by their present functional

activity, no decrease can take place. Again, if we trace up the external

organs of smell through fishes,[7] reptiles, ungulate mammals and

unguiculate mammals, to man, we perceive a general tendency to

coalescence in the median line; and on comparing the savage with the

civilized, or the infant with the adult, we see this approach of the

nostrils carried furthest in the most perfect of the species. But since

the septum which divides them has the function both of an evaporating

surface for the lachrymal secretion, and of a ramifying surface for a

nerve ancillary to that of smell, it does not disappear entirely: the

integration remains incomplete. These and other like instances do not

however militate against the hypothesis. They merely show that the

tendency is sometimes antagonized by other tendencies. Bearing in mind

which qualification, we may say, that as differentiation of parts is

connected with difference of function, so there appears to be a

connexion between integration of parts and sameness of function.

* * * * *

Closely related to the general truth that the evolution of all organisms

is carried on by combined differentiations and integrations, is another

general truth, which physiologists appear not to have recognized. When

we look at the organic world as a whole, we may observe that, on passing

from lower to higher forms, we pass to forms which are not only

characterized by a greater differentiation of parts, but are at the same

time more completely differentiated from the surrounding medium. This

truth may be contemplated under various aspects.

In the first place it is illustrated in _structure_. The advance from

the homogeneous to the heterogeneous itself involves an increasing

distinction from the inorganic world. In the lowest _Protozoa_, as some

of the Rhizopods, we have a homogeneity approaching to that of air,

water, or earth; and the ascent to organisms of greater and greater

complexity of structure, is an ascent to organisms which are in that

respect more strongly contrasted with the relatively structureless

masses in the environment.

In _form_ again we see the same truth. A general characteristic of

inorganic matter is its indefiniteness of form, and this is also a

characteristic of the lower organisms, as compared with the higher.

Speaking generally, plants are less definite than animals, both in shape

and size--admit of greater modifications from variations of position and

nutrition. Among animals, the _Amoeba_ and its allies are not only

almost structureless, but are amorphous; and the irregular form is

constantly changing. Of the organisms resulting from the aggregation of

amoeba-like creatures, we find that while some assume a certain

definiteness of form, in their compound shells at least, others, as the

Sponges, are irregular. In the Zoophytes and in the _Polyzoa_, we see

compound organisms, most of which have modes of growth not more

determinate than those of plants. But among the higher animals, we find

not only that the mature shape of each species is quite definite, but

that the individuals of each species differ very little in size.

A parallel increase of contrast is seen in _chemical composition_. With

but few exceptions, and those only partial ones, the lowest animal and

vegetal forms are inhabitants of the water; and water is almost their

sole constituent. Dessicated _Protophyta_ and _Protozoa_ shrink into

mere dust; and among the acalephes we find but a few grains of solid

matter to a pound of water. The higher aquatic plants, in common with

the higher aquatic animals, possessing as they do much greater tenacity

of substance, also contain a greater proportion of the organic elements;

and so are chemically more unlike their medium. And when we pass to the

superior classes of organisms--land plants and land animals--we find

that, chemically considered, they have little in common either with the

earth on which they stand or the air which surrounds them.

In _specific gravity_, too, we may note the like. The very simplest

forms, in common with the spores and gemmules of the higher ones, are as

nearly as may be of the same specific gravity as the water in which they

float; and though it cannot be said that among aquatic creatures

superior specific gravity is a standard of general superiority, yet we

may fairly say that the superior orders of them, when divested of the

appliances by which their specific gravity is regulated, differ more

from water in their relative weights than do the lower. In terrestrial

organisms, the contrast becomes extremely marked. Trees and plants, in

common with insects, reptiles, mammals, birds, are all of a specific

gravity considerably less than the earth and immensely greater than the

air.

We see the law similarly fulfilled in respect of _temperature_. Plants

generate but an extremely small quantity of heat, which is to be

detected only by delicate experiments; and practically they may be

considered as being in this respect like their environment. Aquatic

animals rise very little above the surrounding water in temperature:

that of the invertebrata being mostly less than a degree above it, and

that of fishes not exceeding it by more than two or three degrees, save

in the case of some large red-blooded fishes, as the tunny, which exceed

it by nearly ten degrees. Among insects, the range is from two to ten

degrees above that of the air: the excess varying according to their

activity. The heat of reptiles is from four to fifteen degrees more than

that of their medium. While mammals and birds maintain a heat which

continues almost unaffected by external variations, and is often greater

than that of the air by seventy, eighty, ninety, and even a hundred

degrees.

Once more, in greater _self-mobility_ a progressive differentiation is

traceable. Dead matter is inert: some form of independent motion is our

most general test of life. Passing over the indefinite border-land

between the animal and vegetable kingdoms, we may roughly class plants

as organisms which, while they exhibit the kind of motion implied in

growth, are not only without locomotive power, but in nearly all cases

are without the power of moving their parts in relation to one another;

and thus are less differentiated from the inorganic world than animals.

Though in those microscopic _Protophyta_ and _Protozoa_ inhabiting the

water--the spores of algae, the gemmules of sponges, and the infusoria

generally--we see locomotion produced by ciliary action; yet this

locomotion, while rapid relatively to their sizes, is absolutely slow.

Of the _Coelenterata_, a great part are either permanently rooted or

habitually stationary, and so have scarcely any self-mobility but that

implied in the relative movements of parts; while the rest, of which the

common jelly-fish serves as a sample, have mostly but little ability to

move themselves through the water. Among the higher aquatic

_Invertebrata_,--cuttle-fishes and lobsters, for instance,--there is a

very considerable power of locomotion; and the aquatic _Vertebrata_ are,

considered as a class, much more active in their movements than the

other inhabitants of the water. But it is only when we come to

air-breathing creatures that we find the vital characteristic of

self-mobility manifested in the highest degree. Flying insects, mammals,

birds, travel with velocities far exceeding those attained by any of the

lower classes of animals; and so are more strongly contrasted with their

inert environments.

Thus, on contemplating the various grades of organisms in their

ascending order, we find them more and more distinguished from their

inanimate media in _structure_, in _form_, in _chemical composition_, in

_specific gravity_, in _temperature_, in _self-mobility_. It is true

that this generalization does not hold with regularity. Organisms which

are in some respects the most strongly contrasted with the inorganic

world, are in other respects less contrasted than inferior organisms. As

a class, mammals are higher than birds; and yet they are of lower

temperature, and have smaller powers of locomotion. The stationary

oyster is of higher organization than the free-swimming medusa; and the

cold-blooded and less heterogeneous fish is quicker in its movements

than the warm-blooded and more heterogeneous sloth. But the admission

that the several aspects under which this increasing contrast shows

itself bear variable ratios to one another, does not negative the

general truth enunciated. Looking at the facts in the mass, it cannot be

denied that the successively higher groups of organisms are severally

characterized, not only by greater differentiation of parts, but also by

greater differentiation from the surrounding medium in sundry other

physical attributes. It would seem that this peculiarity has some

necessary connexion with superior vital manifestations. One of those

lowly gelatinous forms which are some of them so transparent and

colourless as to be with difficulty distinguished from the water they

float in, is not more like its medium in chemical, mechanical, optical,

thermal, and other properties, than it is in the passivity with which it

submits to all the actions brought to bear on it; while the mammal does

not more widely differ from inanimate things in these properties than it

does in the activity with which it meets surrounding changes by

compensating changes in itself. Between these two extremes, we see a

tolerably constant ratio between these two kinds of contrast. In

proportion as an organism is physically like its environment it remains

a passive partaker of the changes going on in its environment; while in

proportion as it is endowed with powers of counteracting such changes,

it exhibits greater unlikeness to its environment.

* * * * *

Thus far we have proceeded inductively, in conformity with established

usage; but it seems to us that much may be done in this and other

departments of biologic inquiry by pursuing the deductive method. The

generalizations at present constituting the science of physiology, both

general and special, have been reached _a posteriori_; but certain

fundamental data have now been discovered, starting from which we may

reason our way _a priori_, not only to some of the truths that have been

ascertained by observation and experiment, but also to some others. The

possibility of such _a priori_ conclusions will be at once recognized on

considering some familiar cases.

Chemists have shown that a necessary condition to vital activity in

animals is oxidation of certain matters contained in the body either as

components or as waste products. The oxygen requisite for this oxidation

is contained in the surrounding medium--air or water, as the case may

be. If the organism be minute, mere contact of its external surface with

the oxygenated medium achieves the requisite oxidation; but if the

organism is bulky, and so exposes a surface which is small in

proportion to its mass, any considerable oxidation cannot be thus

achieved. One of two things is therefore implied. Either this bulky

organism, receiving no oxygen but that absorbed through its integument,

must possess but little vital activity; or else, if it possesses much

vital activity, there must be some extensive ramified surface, internal

or external, through which adequate aeration may take place--a

respiratory apparatus. That is to say, lungs, or gills, or branchiae, or

their equivalents, are predicable _a priori_ as possessed by all active

creatures of any size.

Similarly with respect to nutriment. There are _entozoa_ which, living

in the insides of other animals, and being constantly bathed by

nutritive fluids, absorb a sufficiency through their outer surfaces; and

so have no need of stomachs, and do not possess them. But all other

animals, inhabiting media that are not in themselves nutritive, but only

contain masses of food here and there, must have appliances by which

these masses of food may be utilized. Evidently mere external contact of

a solid organism with a solid portion of nutriment, could not result in

the absorption of it in any moderate time, if at all. To effect

absorption, there must be both a solvent or macerating action, and an

extended surface fit for containing and imbibing the dissolved products:

there must be a digestive cavity. Thus, given the ordinary conditions of

animal life, and the possession of stomachs by all creatures living

under these conditions may be deductively known.

Carrying out the train of reasoning still further, we may infer the

existence of a vascular system or something equivalent to it, in all

creatures of any size and activity. In a comparatively small inert

animal, such as the hydra, which consists of little more than a sac

having a double wall--an outer layer of cells forming the skin, and an

inner layer forming the digestive and absorbent surface--there is no

need for a special apparatus to diffuse through the body the aliment

taken up; for the body is little more than a wrapper to the food it

encloses. But where the bulk is considerable, or where the activity is

such as to involve much waste and repair, or where both these

characteristics exist, there is a necessity for a system of

blood-vessels. It is not enough that there be adequately extensive

surfaces for absorption and aeration; for in the absence of any means of

conveyance, the absorbed elements can be of little or no use to the

organism at large. Evidently there must be channels of communication.

When, as in the _Medusae_, we find these channels of communication

consisting simply of branched canals opening out of the stomach and

spreading through the disk, we may know, _a priori_, that such creatures

are comparatively inactive; seeing that the nutritive liquid thus

partially distributed throughout their bodies is crude and dilute, and

that there is no efficient appliance for keeping it in motion.

Conversely, when we meet with a creature of considerable size which

displays much vivacity, we may know, _a priori_, that it must have an

apparatus for the unceasing supply of concentrated nutriment, and of

oxygen, to every organ--a pulsating vascular system.

It is manifest, then, that setting out from certain known fundamental

conditions to vital activity, we may deduce from them sundry of the

chief characteristics of organized bodies. Doubtless these known

fundamental conditions have been inductively established. But what we

wish to show is that, given these inductively-established primary facts

in physiology, we may with safety draw certain general deductions from

them. And, indeed, the legitimacy of such deductions, though not

formally acknowledged, is practically recognized in the convictions of

every physiologist, as may be readily proved. Thus, were a physiologist

to find a creature exhibiting complex and variously co-ordinated

movements, and yet having no nervous system; he would be less astonished

at the breach of his empirical generalization that all such creatures

have nervous systems, than at the disproof of his unconscious deduction

that all creatures exhibiting complex and variously co-ordinated

movements must have an "internuncial" apparatus by which the

co-ordination may be effected. Or were he to find a creature having

blood rapidly circulated and rapidly aerated, but yet showing a low

temperature, the proof so afforded that active change of matter is not,

as he had inferred from chemical data, the cause of animal heat, would

stagger him more than would the exception to a constantly-observed

relation. Clearly, then, the _a priori_ method already plays a part in

physiological reasoning. If not ostensibly employed as a means of

reaching new truths, it is at least privately appealed to for

confirmation of truths reached _a posteriori_.

But the illustrations above given go far to show, that it may to a

considerable extent be safely used as an independent instrument of

research. The necessities for a nutritive system, a respiratory system,

and a vascular system, in all animals of size and vivacity, seem to us

legitimately inferable from the conditions to continued vital activity.

Given the physical and chemical data, and these structural peculiarities

may be deduced with as much certainty as may the hollowness of an iron

ball from its power of floating in water.

It is not, of course, asserted that the more _special_ physiological

truths can be deductively reached. The argument by no means implies

this. Legitimate deduction presupposes adequate data; and in respect to

the _special_ phenomena of organic growth, structure, and function,

adequate data are unattainable, and will probably ever remain so. It is

only in the case of the more _general_ physiological truths, such as

those above instanced, where we have something like adequate data, that

deductive reasoning becomes possible.

And here is reached the stage to which the foregoing considerations are

introductory. We propose now to show that there are certain still more

general attributes of organized bodies, which are deducible from certain

still more general attributes of things.

* * * * *

In an essay on "Progress: its Law and Cause," elsewhere published,[8] we

have endeavoured to show that the transformation of the homogeneous into

the heterogeneous, in which all progress, organic or other, essentially

consists, is consequent on the production of many effects by one

cause--many changes by one force. Having pointed out that this is a law

of all things, we proceeded to show deductively that the multiform

evolutions of the homogeneous into the heterogeneous--astronomic,

geologic, ethnologic, social, &c.,--were explicable as consequences. And

though in the case of organic evolution, lack of data disabled us from

specifically tracing out the progressive complication as due to the

multiplication of effects; yet, we found sundry indirect evidences that

it was so. Now in so far as this conclusion, that organic evolution

results from the decomposition of each expended force into several

forces, was inferred from the general law previously pointed out, it was

an example of deductive physiology. The particular was concluded from

the universal.

We here propose in the first place to show, that there is another

general truth closely connected with the above; and in common with it

underlying explanations of all progress, and therefore the progress of

organisms--a truth which may indeed be considered as taking precedence

of it in respect of time, if not in respect of generality. This truth

is, that _the condition of homogeneity is a condition of unstable

equilibrium_.

The phrase _unstable equilibrium_ is one used in mechanics to express

a balance of forces of such kind, that the interference of any further

force, however minute, will destroy the arrangement previously existing,

and bring about a different arrangement. Thus, a stick poised on its

lower end is in unstable equilibrium: however exactly it may be placed

in a perpendicular position, as soon as it is left to itself it begins,

at first imperceptibly and then visibly, to lean on one side, and with

increasing rapidity falls into another position. Conversely, a stick

suspended from its upper end is in stable equilibrium: however much

disturbed, it will return to the same position. Our meaning is, then,

that the state of homogeneity, like the state of the stick poised on its

lower end, is one that cannot be maintained; and that hence results the

first step in its gravitation towards the heterogeneous. Let us take a

few illustrations.

Of mechanical ones the most familiar is that of the scales. If

accurately made and not clogged by dirt or rust, a pair of scales cannot

be perfectly balanced: eventually one scale will descend and the other

ascend--they will assume a heterogeneous relation. Again, if we sprinkle

over the surface of a liquid a number of equal-sized particles, having

an attraction for one another, they will, no matter how uniformly

distributed, by and by concentrate irregularly into groups. Were it

possible to bring a mass of water into a state of perfect homogeneity--a

state of complete quiescence, and exactly equal density throughout--yet

the radiation of heat from neighbouring bodies, by affecting differently

its different parts, would soon produce inequalities of density and

consequent currents; and would so render it to that extent

heterogeneous. Take a piece of red-hot matter, and however evenly heated

it may at first be, it will quickly cease to be so: the exterior,

cooling faster than the interior, will become different in temperature

from it. And the lapse into heterogeneity of temperature, so obvious in

this extreme case, is ever taking place more or less in all cases. The

actions of chemical forces supply other illustrations. Expose a

fragment of metal to air or water, and in course of time it will be

coated with a film of oxide, carbonate, or other compound: its outer

parts will become unlike its inner parts. Thus, every homogeneous

aggregate of matter tends to lose its balance in some way or

other--either mechanically, chemically, thermally or electrically; and

the rapidity with which it lapses into a non-homogeneous state is simply

a question of time and circumstances. Social bodies illustrate the law

with like constancy. Endow the members of a community with equal

properties, positions, powers, and they will forthwith begin to slide

into inequalities. Be it in a representative assembly, a railway board,

or a private partnership, the homogeneity, though it may continue in

name, inevitably disappears in reality.

The instability thus variously illustrated becomes still more manifest

if we consider its rationale. It is consequent on the fact that the

several parts of any homogeneous mass are necessarily exposed to

different forces--forces which differ either in their kinds or amounts;

and being exposed to different forces they are of necessity differently

modified. The relations of outside and inside, and of comparative

nearness to neighbouring sources of influence, imply the reception of

influences which are unlike in quantity or quality or both; and it

follows that unlike changes will be wrought in the parts dissimilarly

acted upon. The unstable equilibrium of any homogeneous aggregate can

thus be shown both inductively and deductively.

And now let us consider the bearing of this general truth on the

evolution of organisms. The germ of a plant or animal is one of these

homogeneous aggregates--relatively homogeneous if not absolutely

so--whose equilibrium is unstable. But it has not simply the ordinary

instability of homogeneous aggregates: it has something more. For it

consists of units which are themselves specially characterized by

instability. The constituent molecules of organic matter are

distinguished by the feebleness of the affinities which hold their

component elements together. They are extremely sensitive to heat,

light, electricity, and the chemical actions of foreign elements; that

is, they are peculiarly liable to be modified by disturbing forces.

Hence then it follows, _a priori_, that a homogeneous aggregate of these

unstable molecules will have an excessive tendency to lose its

equilibrium. It will have a quite special liability to lapse into a

non-homogeneous state. It will rapidly gravitate towards heretogeneity.

Moreover, the process must repeat itself in each of the subordinate

groups of organic units which are differentiated by the modifying

forces. Each of these subordinate groups, like the original group, must

gradually, in obedience to the influences acting on it, lose its balance

of parts--must pass from a uniform into a multiform state. And so on

continuously.

Thus, starting from the general laws of things, and the known chemical

attributes of organic matter, we may conclude deductively that the

homogeneous germs of organisms have a peculiar proclivity towards a

non-homogeneous state; which may be either the state we call

decomposition, or the state we call organization.

* * * * *

At present we have reached a conclusion only of the most general nature.

We merely learn that _some_ kind of heterogeneity is inevitable; but as

yet there is nothing to tell us _what_ kind. Besides that _orderly_

heterogeneity which distinguishes organisms, there is the _disorderly_

or _chaotic_ heterogeneity, into which a loose mass of inorganic matter

lapses; and at present no reason has been given why the homogeneous germ

of a plant or animal should not lapse into the disorderly instead of the

orderly heterogeneity. But by pursuing still further the line of

argument hitherto followed we shall find a reason.

We have seen that the instability of homogeneous aggregates in general,

and of organic ones in particular, is consequent on the various ways and

degrees in which their constituent parts are exposed to the disturbing

forces brought to bear on them: their parts are differently acted upon,

and therefore become different. Manifestly, then, a rationale of the

special changes which a germ undergoes, must be sought in the particular

relations which its several parts bear to each other and to their

environment. However it may be masked, we may suspect the fundamental

principle of organization to be, that the many like units forming a germ

acquire those kinds and degrees of unlikeness which their respective

positions entail.

Take a mass of unorganized but organizable matter--either the body of

one of the lowest living forms, or the germ of one of the higher.

Consider its circumstances. It is immersed in water or air; or it is

contained within a parent organism. Wherever placed, however, its outer

and inner parts stand differently related to surrounding

existences--nutriment, oxygen, and the various stimuli. But this is not

all. Whether it lies quiescent at the bottom of the water, whether it

moves through the water preserving some definite attitude, or whether it

is in the inside of an adult; it equally results that certain parts of

its surface are more directly exposed to surrounding agencies than other

parts--in some cases more exposed to light, heat, or oxygen, and in

others to the maternal tissues and their contents. The destruction of

its original equilibrium is therefore certain. It may take place in one

of two ways. Either the disturbing forces may be such as to overbalance

the affinities of the organic elements, in which case there results that

chaotic heterogeneity known as decomposition; or, as is ordinarily the

case, such changes are induced as do not destroy the organic compounds,

but only modify them: the parts most exposed to the modifying forces

being most modified. Hence result those first differentiations which

constitute incipient organization. From the point of view thus reached,

suppose we look at a few cases: neglecting for the present all

consideration of the tendency to assume the inherited type.

Note first what appear to be exceptions, as the _Amoeba_. In this

creature and its allies, the substance of the jelly-like body remains

throughout life unorganized--undergoes no permanent differentiations.

But this fact, which seems directly opposed to our inference, is really

one of the most significant evidences of its truth. For what is the

peculiarity of the Rhizopods, exemplified by the _Amoeba_? They

undergo perpetual and irregular changes of shape--they show no

persistent relations of parts. What lately formed a portion of the

interior is now protruded, and, as a temporary limb, is attached to some

object it happens to touch. What is now a part of the surface will

presently be drawn, along with the atom of nutriment sticking to it,

into the centre of the mass. Thus there is an unceasing interchange of

places; and the relations of inner and outer have no settled existence.

But by the hypothesis, it is only in virtue of their unlike positions

with respect to modifying forces, that the originally-like units of a

living mass become unlike. We must not therefore expect any established

differentiation of parts in creatures which exhibit no established

differences of position in their parts.

This negative evidence is borne out by abundant positive evidence. When

we turn from these ever-changing specks of living jelly to organisms

having unchanging distributions of substance, we find differences of

tissue corresponding to differences of relative position. In all the

higher _Protozoa_, as also in the _Protophyta_, we meet with a

fundamental differentiation into cell-membrane and cell-contents,

answering to that fundamental contrast of conditions implied by the

words outside and inside. And on passing from what are roughly classed

as unicellular organisms to the lowest of those which consist of

aggregated cells, we equally observe the connexion between structural

differences and differences of circumstance. In the sponge, permeated

throughout by currents of sea-water, the absence of definite

organization corresponds with the absence of definite unlikeness of

conditions. In the _Thalassicolla_ of Professor Huxley--a transparent,

colourless body, found floating passively at the surface of the sea, and

consisting essentially of "a mass of cells united by jelly"--there is

displayed a rude structure obviously subordinated to the primary

relations of centre and surface: in all of its many and important

varieties, the parts exhibit a more or less concentric arrangement.

After this primary modification, by which the outer tissues are

differentiated from the inner, the next in order of constancy and

importance is that by which some part of the outer tissues is

differentiated from the rest; and this corresponds with the almost

universal fact that some part of the outer tissues is more directly

exposed to certain environing influences than the rest. Here, as before,

the apparent exceptions are extremely significant. Some of the lowest

vegetable organisms, as the _Hematococci_ and _Protococci_, evenly

imbedded in a mass of mucus, or dispersed through the Arctic snow,

display no differentiations of surface: the several parts of the surface

being subjected to no definite contrasts of conditions. The

_Thalassicolla_ above mentioned, unfixed, and rolled about by the waves,

presents all its sides successively to the same agencies; and all its

sides are alike. A ciliated sphere like the _Volvox_ has no parts of its

periphery unlike other parts; and it is not to be expected that it

should have; seeing that as it revolves in all directions, it does not,

in traversing the water, permanently expose any part to special

conditions. But when we come to creatures that are either fixed, or

while moving, severally preserve a definite attitude, we no longer find

uniformity of surface. The gemmule of a Zoophyte, which during its

locomotive stage is distinguishable only into outer and inner tissues,

no sooner takes root than its upper end begins to assume a different

structure from its lower. The free-swimming embryo of an aquatic

annelid, being ovate and not ciliated all over, moves with one end

foremost; and its differentiations proceed in conformity with this

contrast of circumstances.

The principle thus displayed in the humbler forms of life, is traceable

during the development of the higher; though being here soon masked by

the assumption of the hereditary type, it cannot be traced far. Thus the

"mulberry-mass" into which a fertilized ovum of a vertebrate animal

first resolves itself, soon begins to exhibit a difference between the

outer and inner parts answering to the difference of circumstances. The

peripheral cells, after reaching a more complete development than the

central ones, coalesce into a membrane enclosing the rest; and then the

cells lying next to these outer ones become aggregated with them, and

increase the thickness of the germinal membrane, while the central cells

liquefy. Again, one part of the germinal membrane presently becomes

distinguishable as the germinal spot; and without asserting that the

cause of this is to be found in the unlike relations which the

respective parts of the germinal membrane bear to environing influences,

it is clear that we have in these unlike relations an element of

disturbance tending to destroy the original homogeneity of the germinal

membrane. Further, the germinal membrane by and by divides into two

layers, internal and external; the one in contact with the liquefied

interior part or yelk, the other exposed to the surrounding fluids: this

contrast of circumstances being in obvious correspondence with the

contrast of structures which follows it. Once more, the subsequent

appearance of the vascular layer between these mucous and serous layers,

as they have been named, admits of a like interpretation. And in this

and the various complications which now begin to show themselves, we may

see coming into play that general law of the multiplication of effects

flowing from one cause, to which the increase of heterogeneity was

elsewhere ascribed.[9]

Confining our remarks, as we do, to the most general facts of

development, we think that some light is thus thrown on them. That the

unstable equilibrium of a homogeneous germ must be destroyed by the

unlike exposure of its several units to surrounding influences, is an _a

priori_ conclusion. And it seems also to be an _a priori_ conclusion,

that the several units thus differently acted upon, must either be

decomposed, or must undergo such modifications of nature as may enable

them to live in the respective circumstances they are thrown into: in

other words--_they must either die or become adapted to their

conditions_. Indeed, we might infer as much without going through the

foregoing train of reasoning. The superficial organic units (be they the

outer cells of a "mulberry-mass," or be they the outer molecules of an

individual cell) must assume the function which their position

necessitates; and assuming this function, must acquire such character as

performance of it involves. The layer of organic units lying in contact

with the yelk must be those through which the yelk is absorbed; and so

must be adapted to the absorbent office. On this condition only does the

process of organization appear possible. We might almost say that just

as some race of animals, which multiplies and spreads into divers

regions of the earth, becomes differentiated into several races through

the adaptation of each to its conditions of life; so, the originally

homogeneous population of cells arising in a fertilized germ-cell,

becomes divided into several populations of cells that grow unlike in

virtue of the unlikeness of their circumstances.

Moreover, it is to be remarked in further proof of our position, that it

finds its clearest and most abundant illustrations where the conditions

of the case are the simplest and most general--where the phenomena are

the least involved: we mean in the production of individual cells. The

structures which presently arise round nuclei in a blastema, and which

have in some way been determined by those nuclei as centres of

influence, evidently conform to the law; for the parts of the blastema

in contact with the nuclei are differently conditioned from the parts

not in contact with them. Again, the formation of a membrane round each

of the masses of granules into which the endochrome of an alga-cell

breaks up, is an instance of analogous kind. And should the

recently-asserted fact that cells may arise round vacuoles in a mass of

organizable substance, be confirmed, another good example will be

furnished; for such portions of substance as bound these vacant spaces

are subject to influences unlike those to which other portions of the

substance are subject. If then we can most clearly trace this law of

modification in these primordial processes, as well as in those more

complex but analogous ones exhibited in the early changes of an ovum, we

have strong reason for thinking that the law is fundamental.

But, as already more than once hinted, this principle, understood in the

simple form here presented, supplies no key to the detailed phenomena of

organic development. It fails entirely to explain generic and specific

peculiarities; and leaves us equally in the dark respecting those more

important distinctions by which families and orders are marked out. Why

two ova, similarly exposed in the same pool, should become the one a

fish, and the other a reptile, it cannot tell us. That from two

different eggs placed under the same hen, should respectively come forth

a duckling and a chicken, is a fact not to be accounted for on the

hypothesis above developed. Here we are obliged to fall back upon the

unexplained principle of hereditary transmission. The capacity possessed

by an unorganized germ of unfolding into a complex adult which repeats

ancestral traits in minute details, and that even when it has been

placed in conditions unlike those of its ancestors, is a capacity

impossible for us to understand. That a microscopic portion of seemingly

structureless matter should embody an influence of such kind, that the

resulting man will in fifty years after become gouty or insane, is a

truth which would be incredible were it not daily illustrated. But

though the _manner_ in which hereditary likeness, in all its

complications, is conveyed, is a mystery passing comprehension, it is

quite conceivable that it is conveyed in subordination to the law of

adaptation above explained; and we are not without reasons for thinking

that it is so. Various facts show that acquired peculiarities resulting

from the adaptation of constitution to conditions, are transmissible to

offspring. Such acquired peculiarities consist of differences of

structure or composition in one or more of the tissues. That is to say,

of the aggregate of similar organic units composing a germ, the group

going to the formation of a particular tissue, will take on the special

character which the adaptation of that tissue to new circumstances had

produced in the parents. We know this to be a general law of organic

modifications. Further, it is the _only_ law of organic modifications of

which we have any evidence.[10] It is not impossible then that it is the

universal law; comprehending not simply those minor modifications which

offspring inherit from recent ancestry, but comprehending also those

larger modifications distinctive of species, genus, order, class, which

they inherit from antecedent races of organisms. And thus it _may be_

that the law of adaptation is the sole law; presiding not only over the

differentiation of any race of organisms into several races, but also

over the differentiation of the race of organic units composing a germ,

into the many races of organic units composing an adult. So understood,

the process gone through by every unfolding organism will consist,

partly in the direct adaptation of its elements to their several

circumstances, and partly in the assumption of characters resulting from

analogous adaptations of the elements of all ancestral organisms.

But our argument does not commit us to any such far-reaching speculation

as this; which we introduce simply as suggested by it, not involved. All

we are here concerned to show, is, that the deductive method aids us in

interpreting some of the more general phenomena of development. That all

homogeneous aggregates are in unstable equilibrium is a universal truth,

from which is deducible the instability of every organic germ. From the

known sensitiveness of organic compounds to chemical, thermal, and other

disturbing forces, we further infer the _unusual_ instability of every

organic germ--a proneness far beyond that of other homogeneous

aggregates to lapse into a heterogeneous state. By the same line of

reasoning we are led to the additional inference, that the first

divisions into which a germ resolves itself, being severally in a state

of unstable equilibrium, are similarly prone to undergo further changes;

and so on continuously. Moreover, we have found it to be equally an _a

priori_ conclusion, that as, in all other cases, the loss of homogeneity

is due to the different degrees and kinds of force brought to bear on

the different parts; so, in this case too, difference of circumstances

is the primary cause of differentiation. Add to which, that as the

several changes undergone by the respective parts thus diversely acted

upon, are changes which do not destroy their vital activity, they must

be changes which bring that vital activity into subordination to the

incident forces--they must be adaptations; and the like must be in some

sense true of all the subsequent changes. Thus by deductive reasoning we

get some insight into the method of organization. However unable we are,

and probably ever shall be, to comprehend the way in which a germ is

made to take on the special form of its race, we may yet comprehend the

general principles which regulate its first modifications; and,

remembering the unity of plan so conspicuous throughout nature, we may

_suspect_ that these principles are in some way concerned in succeeding

modifications.

* * * * *

A controversy now going on among zoologists, opens yet another field for

the application of the deductive method. We believe that the question

whether there does or does not exist a _necessary correlation_ among the

several parts of an organism is determinable _a priori_.

Cuvier, who first asserted this necessary correlation, professed to base

his restorations of extinct animals upon it. Geoffroy St. Hilaire and

De Blainville, from different points of view, contested Cuvier's

hypothesis; and the discussion, which has much interest as bearing on

paleontology, has been recently revived under a somewhat modified form:

Professors Huxley and Owen being respectively the assailant and defender

of the hypothesis.

Cuvier says--"Comparative anatomy possesses a principle whose just

development is sufficient to dissipate all difficulties; it is that of

the correlation of forms in organized beings, by means of which every

kind of organized being might, strictly speaking, be recognized by a

fragment of any of its parts. Every organized being constitutes a whole,

a single and complete system, whose parts mutually correspond and concur

by their reciprocal reaction to the same definite end. None of these

parts can be changed without affecting the others; and consequently each

taken separately, indicates and gives all the rest." He then gives

illustrations: arguing that the carnivorous form of tooth necessitating

a certain action of the jaw, implies a particular form in its condyles;

implies also limbs fit for seizing and holding prey; therefore implies

claws, a certain structure of the leg-bones, a certain form of

shoulder-blade. Summing up he says, that "the claw, the scapula, the

condyle, the femur, and all the other bones, taken separately, will give

the tooth or one another; and by commencing with any one, he who had a

rational conception of the laws of the organic economy, could

reconstruct the whole animal."

It will be seen that the method of restoration here contended for, is

based on the alleged physiological necessity of the connexion between

these several peculiarities. The argument used is, not that a scapula of

a certain shape may be recognized as having belonged to a carnivorous

mammal because we always find that carnivorous mammals _do_ possess such

scapulas; but the argument is that they _must_ possess them, because

carnivorous habits would be impossible without them. And in the above

quotation Cuvier asserts that the necessary correlation which he

considers so obvious in these cases, exists throughout the system:

admitting, however, that in consequence of our limited knowledge of

physiology we are unable in many cases to trace this necessary

correlation, and are obliged to base our conclusions upon observed

coexistences, of which we do not understand the reason, but which we

find invariable.

Now Professor Huxley has recently shown that, in the first place, this

empirical method, which Cuvier introduces as quite subordinate, and to

be used only in aid of the rational method, is really the method which

Cuvier habitually employed--the so-called rational method remaining

practically a dead letter; and, in the second place, he has shown that

Cuvier himself has in several places so far admitted the inapplicability

of the rational method, as virtually to surrender it as a method. But

more than this, Professor Huxley contends that the alleged necessary

correlation is not true. Quite admitting the physiological dependence of

parts on each other, he denies that it is a dependence of a kind which

could not be otherwise. "Thus the teeth of a lion and the stomach of

the animal are in such relation that the one is fitted to digest the

food which the other can tear, they are physiologically correlated; but

we have no reason for affirming this to be a necessary physiological

correlation, in the sense that no other could equally fit its possessor

for living on recent flesh. The number and form of the teeth might have

been quite different from that which we know them to be, and the

construction of the stomach might have been greatly altered; and yet the

functions of these organs might have been equally well performed."

Thus much is needful to give an idea of the controversy. It is not here

our purpose to go more at length into the evidence cited on either side.

We simply wish to show that the question may be settled deductively.

Before going on to do this, however, let us briefly notice two

collateral points.

In his defence of the Cuvierian doctrine, Professor Owen avails himself

of the _odium theologicum_. He attributes to his opponents "the

insinuation and masked advocacy of the doctrine subversive of a

recognition of the Higher Mind." Now, saying nothing about the

questionable propriety of thus prejudging an issue in science, we think

this is an unfortunate accusation. What is there in the hypothesis of

_necessary_, as distinguished from _actual_, correlation of parts, which

is particularly in harmony with Theism? Maintenance of the _necessity_,

whether of sequences or of coexistences, is commonly thought rather a

derogation from divine power than otherwise. Cuvier says--"None of these

parts can be changed without affecting the others; and consequently,

each taken separately, indicates and gives all the rest." That is to

say, in the nature of things the correlation _could not_ have been

otherwise. On the other hand, Professor Huxley says we have no warrant

for asserting that the correlation _could not_ have been otherwise; but

have not a little reason for thinking that the same physiological ends

might have been differently achieved. The one doctrine limits the

possibilities of creation; the other denies the implied limit. Which,

then, is most open to the charge of covert Atheism?

On the other point we lean to the opinion of Professor Owen. We agree

with him in thinking that where a rational correlation (in the highest

sense of the term) can be made out, it affords a better basis for

deduction than an empirical correlation ascertained only by accumulated

observations. Premising that by rational correlation is not meant one in

which we can trace, or think we can trace, a design, but one of which

the negation is inconceivable (and this is the species of correlation

which Cuvier's principle implies); then we hold that our knowledge of

the correlation is of a more certain kind than where it is simply

inductive. We think that Professor Huxley, in his anxiety to avoid the

error of making Thought the measure of Things, does not sufficiently

bear in mind the fact, that as our notion of necessity is determined by

some absolute uniformity pervading all orders of our experiences, it

follows that an organic correlation which cannot be conceived otherwise,

is guaranteed by a much wider induction than one ascertained only by the

observation of organisms. But the truth is, that there are relatively

few organic correlations of which the negation is inconceivable. If we

find the skull, vertebrae, ribs, and phalanges of some quadruped as large

as an elephant; we may indeed be certain that the legs of this quadruped

were of considerable size--much larger than those of a rat; and our

reason for conceiving this correlation as necessary, is, that it is

based, not only upon our experiences of moving organisms, but upon all

our mechanical experiences relative to masses and their supports. But

even were there many physiological correlations really of this order,

which there are not, there would be danger in pursuing this line of

reasoning, in consequence of the liability to include within the class

of truly necessary correlations, those which are not such. For instance,

there would seem to be a necessary correlation between the eye and the

surface of the body: light being needful for vision, it might be

supposed that every eye must be external. Nevertheless it is a fact that

there are creatures, as the _Cirrhipedia_, having eyes (not very

efficient ones, it may be) deeply imbedded within the body. Again, a

necessary correlation might be assumed between the dimensions of the

mammalian uterus and those of the pelvis. It would appear impossible

that in any species there should exist a well-developed uterus

containing a full-sized foetus, and yet that the arch of the pelvis

should be too small to allow the foetus to pass. And were the only

mammal having a very small pelvic arch, a fossil one, it would have been

inferred, on the Cuvierian method, that the foetus must have been born

in a rudimentary state; and that the uterus must have been

proportionally small. But there happens to be an extant mammal having an

undeveloped pelvis--the mole--which presents us with a fact that saves

us from this erroneous inference. The young of the mole are not born

through the pelvic arch at all; but in front of it! Thus, granting that

some quite _direct_ physiological correlations may be necessary, we see

that there is great risk of including among them some which are not.

With regard to the great mass of the correlations, however, including

all the _indirect_ ones, Professor Huxley seems to us warranted in

denying that they are necessary; and we now propose to show deductively

the truth of his thesis. Let us begin with an analogy.

Whoever has been through an extensive iron-works, has seen a gigantic

pair of shears worked by machinery, and used for cutting in two, bars of

iron that are from time to time thrust between its blades. Supposing

these blades to be the only visible parts of the apparatus, anyone

observing their movements (or rather the movement of one, for the other

is commonly fixed), will see from the manner in which the angle

increases and decreases, and from the curve described by the moving

extremity, that there must be some centre of motion--either a pivot or

an external box equivalent to it. This may be regarded as a necessary

correlation. Moreover, he might infer that beyond the centre of motion

the moving blade was produced into a lever, to which the power was

applied; but as another arrangement is just possible, this could not be

called anything more than a highly probable correlation. If now he went

a step further, and asked how the reciprocal movement was given to the

lever, he would perhaps conclude that it was given by a crank. But if he

knew anything of mechanics, he would know that it might possibly be

given by an eccentric. Or again, he would know that the effect could be

achieved by a cam. That is to say, he would see that there was no

necessary correlation between the shears and the remoter parts of the

apparatus. Take another case. The plate of a printing-press is required

to move up and down to the extent of an inch or so; and it must exert

its greatest pressure when it reaches the extreme of its downward

movement. If now anyone will look over the stock of a printing-press

maker, he will see half a dozen different mechanical arrangements by

which these ends are achieved; and a machinist would tell him that as

many more might readily be invented. If, then, there is no necessary

correlation between the special parts of a machine, still less is there

between those of an organism.

From a converse point of view the same truth is manifest. Bearing in

mind the above analogy, it will be foreseen that an alteration in one

part of an organism will not necessarily entail _some one specific set

of alterations in the other parts_. Cuvier says, "None of these parts

can be changed without affecting the others; and consequently, each

taken separately, indicates and gives all the rest." The first of these

propositions may pass, but the second, which it is alleged follows from

it, is not true; for it implies that "all the rest" can be severally

affected in only one way and degree, whereas they can be affected in

many ways and degrees. To show this, we must again have recourse to a

mechanical analogy.

If you set a brick on end and thrust it over, you can predict with

certainty in what direction it will fall, and what attitude it will

assume. If, again setting it up, you put another on the top of it, you

can no longer foresee with accuracy the results of an overthrow; and on

repeating the experiment, no matter how much care is taken to place the

bricks in the same positions, and to apply the same degree of force in

the same direction, the effects will on no two occasions be exactly

alike. And in proportion as the aggregation is complicated by the

addition of new and unlike parts, will the results of any disturbance

become more varied and incalculable. The like truth is curiously

illustrated by locomotive engines. It is a fact familiar to mechanical

engineers and engine-drivers, that out of a number of engines built as

accurately as possible to the same pattern, no two will act in just the

same manner. Each will have its peculiarities. The play of actions and

reactions will so far differ, that under like conditions each will

behave in a somewhat different way; and every driver has to learn the

idiosyncrasies of his own engine before he can work it to the greatest

advantage. In organisms themselves this indefiniteness of mechanical

reaction is clearly traceable. Two boys throwing stones will always

differ more or less in their attitudes, as will two billiard-players.

The familiar fact that each individual has a characteristic gait,

illustrates the point still better. The rhythmical motion of the leg is

simple, and on the Cuvierian hypothesis, should react on the body in

some uniform way. But in consequence of those slight differences of

structure which consist with identity of species, no two individuals

make exactly similar movements either of the trunk or the arms. There

is always a peculiarity recognizable by their friends.

When we pass to disturbing forces of a non-mechanical kind, the same

truth becomes still more conspicuous. Expose several persons to a

drenching storm; and while one will subsequently feel no appreciable

inconvenience, another will have a cough, another a catarrh, another an

attack of diarrhoea, another a fit of rheumatism. Vaccinate several

children of the same age with the same quantity of virus, applied to the

same part, and the symptoms will not be quite alike in any of them,

either in kind or intensity; and in some cases the differences will be

extreme. The quantity of alcohol which will send one man to sleep, will

render another unusually brilliant--will make this maudlin, and that

irritable. Opium will produce either drowsiness or wakefulness: so will

tobacco.

Now in all these cases--mechanical and other--some force is brought to

bear primarily on one part of an organism, and secondarily on the rest;

and, according to the doctrine of Cuvier, the rest ought to be affected

in a specific way. We find this to be by no means the case. The original

change produced in one part does not stand in any necessary correlation

with every one of the changes produced in the other parts; nor do these

stand in any necessary correlation with one another. The functional

alteration which the disturbing force causes in the organ directly acted

upon, does not involve some _particular set_ of functional alterations

in the other organs; but will be followed by some one out of various

sets. And it is a manifest corollary, that any _structural alteration_

which may eventually be produced in the one organ, will not be

accompanied by _some particular set of structural alterations_ in the

other organs. There will be no necessary correlation of forms.

Thus Paleontology must depend upon the empirical method. A fossil

species that was obliged to change its food or habits of life, did not

of necessity undergo the particular set of modifications exhibited; but,

under some slight change of predisposing causes--as of season or

latitude--might have undergone some other set of modifications: the

determining circumstance being one which, in the human sense, we call

fortuitous.

May we not say then, that the deductive method elucidates this vexed

question in physiology; while at the same time our argument collaterally

exhibits the limits within which the deductive method is applicable. For

while we see that this extremely _general_ question may be

satisfactorily dealt with deductively; the conclusion arrived at itself

implies that the more _special_ phenomena of organization cannot be so

dealt with.

* * * * *

There is yet another method of investigating the general truths of

physiology--a method to which physiology already owes one luminous idea,

but which is not at present formally recognized as a method. We refer to

the comparison of physiological phenomena with social phenomena.

The analogy between individual organisms and the social organism, is one

that has from early days occasionally forced itself on the attention of

the observant. And though modern science does not countenance those

crude ideas of this analogy which have been from time to time expressed

since the Greeks flourished; yet it tends to show that there _is_ an

analogy, and a remarkable one. While it is becoming clear that there are

not those special parallelisms between the constituent parts of a man

and those of a nation, which have been thought to exist; it is also

becoming clear that the general principles of development and structure

displayed in organized bodies are displayed in societies also. The

fundamental characteristic both of societies and of living creatures,

is, that they consist of mutually-dependent parts; and it would seem

that this involves a community of various other characteristics. Those

who are acquainted with the broad facts of both physiology and

sociology, are beginning to recognize this correspondence not as a

plausible fancy, but as a scientific truth. And we are strongly of

opinion that it will by and by be seen to hold to an extent which few at

present suspect.

Meanwhile, if any such correspondence exists, it is clear that

physiology and sociology will more or less interpret each other. Each

affords its special facilities for inquiry. Relations of cause and

effect clearly traceable in the social organism, may lead to the search

for analogous ones in the individual organism; and may so elucidate what

might else be inexplicable. Laws of growth and function disclosed by the

pure physiologist, may occasionally give us the clue to certain social

modifications otherwise difficult to understand. If they can do no more,

the two sciences can at least exchange suggestions and confirmations;

and this will be no small aid. The conception of "the physiological

division of labour," which political economy has already supplied to

physiology, is one of no small value. And probably it has others to

give.

In support of this opinion, we will now cite cases in which such aid is

furnished. And in the first place, let us see whether the facts of

social organization do not afford additional support to some of the

doctrines set forth in the foregoing parts of this article.

One of the propositions supported by evidence was that in animals the

process of development is carried on, not by differentiations only, but

by subordinate integrations. Now in the social organism we may see the

same duality of process; and further, it is to be observed that the

integrations are of the same three kinds. Thus we have integrations

which arise from the simple growth of adjacent parts that perform like

functions: as, for instance, the coalescence of Manchester with its

calico-weaving suburbs. We have other integrations which arise when, out

of several places producing a particular commodity, one monopolizes

more and more of the business, and leaves the rest to dwindle: witness

the growth of the Yorkshire cloth-districts at the expense of those in

the west of England; or the absorption by Staffordshire of the

pottery-manufacture, and the consequent decay of the establishments that

once flourished at Worcester, Derby, and elsewhere. And we have those

yet other integrations which result from the actual approximation of the

similarly-occupied parts: whence result such facts as the concentration

of publishers in Paternoster Row, of lawyers in the Temple and

neighbourhood, of corn-merchants about Mark Lane, of civil engineers in

Great George Street, of bankers in the centre of the city. Finding thus

that in the evolution of the social organism, as in the evolution of

individual organisms, there are integrations as well as

differentiations, and moreover that these integrations are of the same

three orders; we have additional reason for considering these

integrations as essential parts of the developmental process, needed to

be included in its formula. And further, the circumstance that in the

social organism these integrations are determined by community of

function, confirms the hypothesis that they are thus determined in the

individual organism.

Again, we endeavoured to show deductively, that the contrasts of parts

first seen in all unfolding embryos, are consequent upon the contrasted

circumstances to which such parts are exposed; that thus, adaptation of

constitution to conditions is the principle which determines their

primary changes; and that, possibly, if we include under the formula

hereditarily-transmitted adaptations, all subsequent differentiations

may be similarly determined. Well, we need not long contemplate the

facts to see that some of the predominant social differentiations are

brought about in an analogous way. As the members of an

originally-homogeneous community multiply and spread, the gradual

separation into sections which simultaneously takes place, manifestly

depends on differences of local circumstances. Those who happen to

live near some place chosen, perhaps for its centrality, as one of

periodical assemblage, become traders, and a town springs up; those who

live dispersed, continue to hunt or cultivate the earth; those who

spread to the sea-shore fall into maritime occupations. And each of

these classes undergoes modifications of character fitting to its

function. Later in the process of social evolution these local

adaptations are greatly multiplied. In virtue of differences of soil and

climate, the rural inhabitants in different parts of the kingdom, have

their occupations partially specialized; and are respectively

distinguished as chiefly producing cattle, or sheep, or wheat, or oats,

or hops, or cider. People living where coal-fields are discovered become

colliers; Cornishmen take to mining because Cornwall is metalliferous;

and the iron-manufacture is the dominant industry where ironstone is

plentiful. Liverpool has assumed the office of importing cotton, in

consequence of its proximity to the district where cotton goods are

made; and for analogous reasons Hull has become the chief port at which

foreign wools are brought in. Even in the establishment of breweries, of

dye-works, of slate-quarries, of brick-yards, we may see the same truth.

So that, both in general and in detail, these industrial specializations

of the social organism which characterize separate districts, primarily

depend on local circumstances. Of the originally-similar units making up

the social mass, different groups assume the different functions which

their respective positions entail; and become adapted to their

conditions. Thus, that which we concluded, _a priori_, to be the leading

cause of organic differentiations, we find, _a posteriori_, to be the

leading cause of social differentiations. Nay further, as we inferred

that possibly the embryonic changes which are not thus directly caused,

are caused by hereditarily-transmitted adaptations; so, we may actually

see that in embryonic societies, such changes as are not due to direct

adaptations, are in the main traceable to adaptations originally

undergone by the parent society. The colonies founded by distinct

nations, while they are alike in exhibiting specializations caused in

the way above described, grow unlike in so far as they take on, more or

less, the organizations of the nations they sprung from. A French

settlement does not develop exactly after the same manner as an English

one; and both assume forms different from those which Roman settlements

assumed. Now the fact that the differentiation of societies is

determined partly by the direct adaptation of their units to local

conditions, and partly by the transmitted influence of like adaptations

undergone by ancestral societies, tends strongly to enforce the

conclusion, otherwise reached, that the differentiation of individual

organisms, similarly results from immediate adaptations compounded with

ancestral adaptations.

From confirmations thus furnished by sociology to physiology, let us now

pass to a suggestion similarly furnished. A factory, or other producing

establishment, or a town made up of such establishments, is an agency

for elaborating some commodity consumed by society at large; and may be

regarded as analogous to a gland or viscus in an individual organism. If

we inquire what is the primitive mode in which one of these producing

establishments grows up, we find it to be this. A single worker, who

himself sells the produce of his labour, is the germ. His business

increasing, he employs helpers--his sons or others; and having done

this, he becomes a vendor not only of his own handiwork, but of that of

others. A further increase of his business compels him to multiply his

assistants, and his sale grows so rapid that he is obliged to confine

himself to the process of selling: he ceases to be a producer, and

becomes simply a channel through which the produce of others is conveyed

to the public. Should his prosperity rise yet higher, he finds that he

is unable to manage even the sale of his commodities, and has to employ

others, probably of his own family, to aid him in selling; so that, to

him as a main channel are now added subordinate channels. Moreover, when

there grow up in one place, as a Manchester or a Birmingham, many

establishments of like kind, this process is carried still further.

There arise factors and buyers, who are the channels through which is

transmitted the produce of many factories; and we believe that primarily

these factors were manufacturers who undertook to dispose of the produce

of smaller houses as well as their own, and ultimately became salesmen

only. Under a converse aspect, all the stages of this development have

been within these few years exemplified in our railway contractors.

There are sundry men now living who illustrate the whole process in

their own persons--men who were originally navvies, digging and

wheeling; who then undertook some small sub-contract, and worked along

with those they paid; who presently took larger contracts, and employed

foremen; and who now contract for whole railways, and let portions to

sub-contractors. That is to say, we have men who were originally

workers, but have finally become the main channels out of which diverge

secondary channels, which again bifurcate into the subordinate channels,

through which flows the money (representing the nutriment) supplied by

society to the actual makers of the railway. Now it seems worth

inquiring whether this is not the original course followed in the

evolution of secreting and excreting organs in an animal. We know that

such is the process by which the liver is developed. Out of the group of

bile-cells forming the germ of it, some centrally-placed ones, lying

next to the intestine, are transformed into ducts through which the

secretion of the peripheral bile-cells is poured into the intestine; and

as the peripheral bile-cells multiply, there similarly arise secondary

ducts emptying themselves into the main ones; tertiary ones into these;

and so on. Recent inquiries show that the like is the case with the

lungs,--that the bronchial tubes are thus formed. But while analogy

suggests that this is the _original_ mode in which such organs are

developed, it at the same time suggests that this does not necessarily

continue to be the mode. For as we find that in the social organism,

manufacturing establishments are no longer commonly developed through

the series of modifications above described, but now mostly arise by the

direct transformation of a number of persons into master, clerks,

foremen, workers, &c.; so the approximate method of forming organs, may

in some cases be replaced by a direct metamorphosis of the organic units

into the destined structure, without any transitional structures being

passed through. That there are organs thus formed is an ascertained

fact; and the additional question which analogy suggests is, whether the

direct method is substituted for the indirect method.

Such parallelisms might be multiplied. And were it possible here to show

in detail the close correspondence between the two kinds of

organization, our case would be seen to have abundant support. But, as

it is, these few illustrations will sufficiently justify the opinion

that study of organized bodies may be indirectly furthered by study of

the body politic. Hints may be expected, if nothing more. And thus we

venture to think that the Inductive Method, usually alone employed by

most physiologists, may not only derive important assistance from the

Deductive Method, but may further be supplemented by the Sociological

Method.