sustain, in respiration, in nutrition, in external and internal movements,

the most complex chemical and physical processes, to develop and build up

through a long series of stages a complete whole from the primitive

beginnings in the germ, to grow, to become mature, and gradually to break

up again, and with all this to repeat in itself the type of its parent,

and to bring forth others like itself, thus perpetuating its own species,

to react effectively to stimuli, to produce protective devices against

injury, and to regenerate lost parts? All this is done by living

organisms, all this is the expression in them of "Life." What is it?

Whence comes it? And how can it be explained?



The problem of the nature of life, of the principle of vitality, is almost

as old as philosophy itself, and from the earliest times in which men

began to ponder over the problem, the same antitheses have been apparent

which we find to-day. Disguised under various catchwords and with the

greatest diversities of expression, the antitheses remain essentially the

same through the centuries, competing with one another, often mingling

curiously, so that from time to time one or other almost disappears, but

always crops up again, so that it seems as if the conflict would be a

never-ending one--the antitheses between the mechanical and the

"vitalistic" view of life. On the one side there is the conviction that

the processes of life may be interpreted in terms of natural processes of

a simple and obvious kind, indeed directly in terms of those which are

most general and most intelligible--namely, the simplest movements of the

smallest particles of matter, which are governed by the same laws as

movement in general. And associated with this is the attempt to take away

any special halo from around the processes of life, to admit even here no

other processes but the mechanical ones, and to explain everything as the

effect of material causes. On the opposite side is the conviction that

vital phenomena occupy a special and peculiar sphere in the world of

natural phenomena, a higher platform; that they cannot be explained by

merely physical or chemical or mechanical factors, and that, if

"explaining" means reducing to terms of such factors, they do in truth

include something inexplicable. These opposing conceptions of the living

and the organic have been contrasted with one another, in most precise

form and exact expression, by Kant in certain chapters of the Kritik der

Urteilskraft, which must be regarded as a classic for our subject.(56) But

as far as their general tendency is concerned, they were already

represented in the nature-philosophies of Democritus on the one hand, and

of Aristotle on the other.



All the essential constituents of the modern mechanical theories are

really to be found in Democritus, the causal interpretation, the denial of

any operative purposes or formative principles, the admission and

assertion of quantitative explanations alone, the denial of qualities, the

reduction of all cosmic developments to the "mechanics of the atom" (even

to attractions and repulsions, thus setting aside the "energies"), the

inevitable necessity of these mechanical sequences, indeed at bottom even

the conviction of the "constancy of the sum of matter and energy." (For,

as he says, "nothing comes out of nothing.") And although he makes the

"soul" the principle of the phenomena of life, that is in no way

contradictory to his general mechanical theory, but is quite congruent

with it. For the "soul" is to him only an aggregation of thinner,

smoother, and rounder atoms, which as such are more mobile, and can, as it

were, quarter themselves in the body, but nevertheless stand in a purely

mechanical relation to it.



Aristotle, who was well aware of the diametrical opposition, represents,

as compared with Democritus, the Socratic-Platonic teleological

interpretation of nature, and in regard to the question of living

organisms his point of view may quite well be designated by the modern

name of "vitalism." Especially in his theory of the vegetable soul, the

essence of vitalism is already contained. It is the {~GREEK SMALL LETTER LAMDA~}{~GREEK SMALL LETTER OMICRON WITH OXIA~}{~GREEK SMALL LETTER GAMMA~}{~GREEK SMALL LETTER OMICRON~}{~GREEK SMALL LETTER FINAL SIGMA~} {~GREEK SMALL LETTER EPSILON WITH PSILI~}{~GREEK SMALL LETTER NU~}{~GREEK SMALL LETTER UPSILON~}{~GREEK SMALL LETTER LAMDA~}{~GREEK SMALL LETTER OMICRON~}{~GREEK SMALL LETTER FINAL SIGMA~} (logos

enhylos), the idea immanent in the matter, the conceptual essence of the

organism, or its ideal whole, which is inherent in it from its beginnings

in the germ, and determines, like a directing law, all its vegetative

processes, and so raises it from a state of "possibility" to one of

"reality." All that we meet with later as "nisus formativus," as

"life-force" (vis vitalis), as "endeavour after an end" (Zielstrebigkeit),

is included in the scope of Aristotelian thought. And he has the advantage

over many of his successors of being very much clearer.(57)



The present state of the problem of life may be regarded as due to a

reaction of biological investigation and opinion from the "vitalistic"

theories which prevailed in the first half of last century, and which were

in turn at once the root and the fruit of the German Nature-philosophy of

that time.



Lotze in his oft-quoted article, "Leben, Lebenskraft" (Life, Vital Force),

in Wagner's "Hand-Woerterbuch der Physiologie," 1842, gave the signal for

this reaction. The change, however, did not take place suddenly. The most

important investigators in their special domain, the physiologist Johannes

Mueller, the chemist Julius Liebig, remained faithful to a modified

vitalistic standpoint. But in the following generation the revolution was

complete and energetic. With Du Bois-Reymond, Virchow, Haeckel, the

anti-vitalistic trend became more definite and more widespread. It had a

powerful ally in the Darwinian theory, which had been promulgated

meanwhile, and at the same time in the increasingly materialistic tendency

of thought, which afforded support to the mechanical system and also

sought foundations in it.



The naturalistic, "mechanical" interpretation of life was so much in the

tenor of Darwin's doctrine that it would have arisen out of it if it had

not existed before. It is so generally regarded as a self-evident and

necessary corollary of the strictly Darwinian doctrine, that it is often

included with it under the name of Darwinism, although Darwin personally

did not devote any attention to the problem of the mechanical

interpretation of life. Any estimate of the value of one must be

associated with an estimate of the other also.



It goes without saying that the theory of life is dependent upon, and in a

large measure consists of physico-chemical interpretations,

investigations, and methods. For ever since the attention of investigators

was directed to the problems of growth, of nutrition, of development and

so on, and particularly as knowledge has passed from primitive and

unmethodical forms to real science, it has been taken as a matter of

course that chemical and physical processes play a large part in life, and

indeed that everything demonstrable, visible, or analysable, does come

about "naturally," as it is said. And from the vitalistic standpoint it

has to be asked whether detailed biological investigation and analysis can

ever accomplish more than the observation and tracing out of these

chemical and physical processes. Anything beyond this will probably be

only the defining and formulating of the limits of its own proper sphere

of inquiry, and a recognition, though no knowledge, of what lies beyond

and of the co-operative factors. The difference between vitalism and the

mechanical theory of life is not, that the one regards the processes in

the organism as opposed to those in the inorganic world while the other

identifies them, but that vitalism regards life as a combination of

chemical and physical processes, with the co-operation and under the

regulation of other principles, while the mechanical theory leaves these

other principles out.



Notwithstanding the many noteworthy reactions, we are bound to regard the

present state of the theory of life as on the whole mechanical. The

majority of experts--not to speak of the popular materialists, and

especially those who, sailing under the flag of materialistic

interpretation, have their ships full of vitalistic contraband--regard as

the ideal of their science an ultimate analysis of the phenomena of life

into mechanical processes, into "mechanics of the atom." They believe in

this ideal, and without concealing that it is still very far off, do not

doubt its ultimate attainability, and regard vitalistic assumptions as

obstacles to the progress of investigation. Moreover, this aspect of the

problem seems likely enough to be permanent with the majority, or, at any

rate, with many naturalists, though it is obviously one-sided. For it has

always been the task of this line of investigation to extend the sphere

within which physical and chemical laws can be validly applied in

interpreting vital processes, and the results reached along this line will

always be so numerous and important that even on psychological grounds the

mechanical point of view has the best chance for the future. Furthermore,

the maxim that all the phenomena of nature must be explained by means of

the simplest factors and according to the smallest possible number of

laws, is usually regarded as one of the most legitimate maxims of science

in general, so that the resolute pertinacity with which many investigators

maintain the entire sufficiency of the mechanical interpretation, far from

being condemned as materialistic fanaticism, must be respected as the

expression of scientific conscience. Even when confidence in the one-sided

mechanical interpretation of vital processes sometimes fails in face of

the great and striking riddles of life, it is to be expected that it will

revive again with each new success, great or small.(58)



The mechanical conception of life which now prevails is made up of the

following characteristics and component elements. These also indicate the

lines along which the arguments are worked out--lines which glimmered

faintly through the mechanical theories of ancient times, but which have

now been definitely formulated and supported by evidence.