The subject of the present course of Gifford Lectures is the relation between the Sciences and Philosophy. I have chosen this subject because the issues which its discussion raises seem to me to be very urgent at the present time, and to enter into our lives and practical affairs at innumerable points. At the same time I am very conscious of the inherent difficulties of my task, and of the shortcomings in intellectual equipment which make it impossible for me to deal adequately with so great a subject. My only excuse for making the present attempt is that other persons would experience to perhaps as great an extent, though in other directions, the shortcomings which I feel so keenly. There may, however, be some advantages in the fact of my being a physiologist; for it is very specially in connection with physiology and its relations to other departments of knowledge that central questions concerning the relations of Science and Philosophy have come to the surface in recent times.

In any one of the Sciences we are dealing primarily with one aspect only of our experience, and confine our immediate scientific conclusions to that aspect only. Let me illustrate this statement, for perhaps it is not at first very evidently true. In the physical sciences, including both physics and chemistry, attention is confined primarily to what we distinguish, whether artificially or not, as inorganic phenomena. It is in the study of phenomena thus distinguished that certain principles seem to be forced upon us as the result of observation; and if we limit our view to the aspect of experience we are dealing with, no other principles may seem to be necessary or in place. But if physical and chemical principles are assumed to cover also the phenomena of life or conscious behaviour, controversy at once ensues, even among physicists and chemists themselves.

The difference between any branch of science and philosophy is that in formulating its conclusions philosophy attempts to take into consideration, not simply a part, but the whole of our experience. That experience includes, for instance, not merely the fact that a physical world is apparently presented to us in experience, but also the fact that this physical world is perceived, and that with the perception of it we perceive ourselves and numerous other living and sentient beings, as well as endless emotional and other experiences which cannot be interpreted as pertaining directly to physical objects. We also perceive what we call values, which are of the last importance in relation to conduct. The task of philosophy is to form as consistent as possible a general conception of this apparently confused collection of experiences, so that we can guide our conduct in accordance with the general conception.

Here philosophy comes into living contact with the principles of the sciences, as well as with religious beliefs. A widespread idea exists that the sciences simply supply incontrovertible facts for the philosophers to make what they can of in conjunction with other independently ascertained facts. A classical and extraordinarily important example of the application of this idea is furnished in Newton's Principia. In that great work the mechanical conception of the visible world is represented as “philosophical” truth. No one believed more firmly than Newton in the existence of an invisible spiritual reality coexistent with material reality; but for Newton physical reality, as he conceived it, was in actual fact reality. Most of the modern civilized world has agreed with him in this conclusion, which has thus become to such an extent part of the generally accepted intellectual outfit of modern times that it is only by great effort, and at the risk of being regarded as mere cranks, that we can bring ourselves to question it.

The practical usefulness within certain limits of Newton's “philosophical” conception of the visible world has been made evident in a thousand ways; but if we accept this conception as final we are at once confronted with difficulties which arise in combining it with the rest of our experience into a consistent whole. For Newton the visible world consisted of “bodies” existing independently of one another in independently existing space, and subject to changes following outside one another in steadily flowing time, the flow of which was assumed to be independent of these changes. For philosophy, however, one of the first questions, pressed home by Berkeley and Hume, was how such a world, if it really existed, could ever come to be perceived or known to exist; and their answer to this question was that such knowledge would be impossible, so that Newton's “philosophical” interpretation of the actually experienced visible world is likewise impossible.

The philosophical arguments of Berkeley, Hume, and their successors are so far removed from the details of what the sciences deal with that it is not from the standpoint of these arguments that I propose to enter upon the consideration of the relations of philosophy to the sciences. Nor do I propose to discuss at any length in this first course what may be called the internal difficulties of the Newtonian conception as applied only to inorganic phenomena, and the modifications which that conception has in recent years been undergoing at the hands of physicists and mathematicians themselves. What I shall attempt is to compare broadly the conclusions reached through observation in connexion with different branches of science or knowledge, and consider to what extent these conclusions are consistent with one another. After this comparison, which I shall endeavour to make in the first course of lectures, it will be possible to take up, as I propose to do in the second course, the question as to what assumptions are needed to harmonize the conclusions of the different sciences, and the relation of these assumptions to the nearer questions to which philosophical enquiry is usually directed, including questions which bear on social life and religious beliefs.

I shall begin this course by an attempt to compare the general principles which seem to be forced upon us in the isolated study of two great departments of natural science—the physical sciences and biology. The physical sciences, which include all that is comprised under the general titles of physics and chemistry, deal primarily with reality as it appears to us in what we distinguish as inorganic phenomena, and apart from the consideration of life, conscious activity, and all that seems to pertain to them specifically. The distinction between physics and chemistry is only one of practical convenience: for we can correctly call chemistry and physical chemistry the physics of atoms and molecules. In any case physics, in dealing with such phenomena as those of electricity, magnetism, radiation, and radio-activity, goes beyond and behind the atoms of ordinary chemical theory.

The biological sciences, on the other hand, deal with distinctive phenomena presented by living organisms and their activities, whether these organisms are classified as plants or animals. The biological sciences do not deal primarily, however, with what we distinguish as conscious activity. However prominently conscious activity seems to be associated with the lives of the higher organisms, we do not take it into account in what is ordinarily called biology. Conscious activity will, therefore, be considered separately in later lectures of this course; and only life in the sense in which we attribute it to what we regard as the unconscious phenomena distinctive of living organisms, whether classified as animal or plants, will be considered at first.

If we neglect for the moment certain of the quite recent developments of physical theory, the broad general assumption made in the physical sciences, and apparently forced on them by observation of inorganic phenomena, is that the visible and tangible world consists of independent and permanent “bodies” or masses, with equally permanent and unchangeable properties, though visible bodies are only aggregates of the elementary bodies known as atoms, or, pressing the analysis further, electrons and protons; that these bodies act upon one another in accordance with their properties; and that the sum of their mutual actions, expressed as energy, can and must be regarded as constant no less than the bodies themselves, expressed as mass. In other words, the principles of the conservation of matter and of energy are assumed to hold good, and can apparently be verified wherever the conditions are such that verification is possible. It is true that quite recent work has shown that the distinction between mass and energy cannot ultimately be upheld; but in ordinary physics and chemistry we interpret our observations in terms of the conceptions of matter and energy.

The first five lectures will be devoted to the consideration of how far the same fundamental conceptions are applicable to the phenomena of life as they ordinarily appear in biological investigation, or what other conceptions are necessary. A preliminary glance at this discussion and its outcome will, I think, be useful as a guide in the present introductory lecture.

It is of course quite evident, and has always been assumed by biologists, that up to a certain point the same general principles can be applied successfully to biological as to physical observations. All biological observations, for instance, are in full accord with the assumption that within living organisms there is neither creation nor loss of substance. Living organisms grow or waste through what we can describe as intake or output of material, and in no other way that has hitherto been demonstrated or is ever now suspected. Similarly, the energy output of an organism depends upon previous energy-intake, as was first pointed out in 1845 by J. R. Mayer,1 in connexion with his general formulation of the principle of conservation of energy, though a satisfactorily exact experimental demonstration of this fact was first given by Rubner in 1893. We can discover no contradiction of these principles in organic phenomena. On the other hand, however, consideration of organic phenomena seems to force us to reconsider the whole conception which we derive from the isolated study of inorganic phenomena, since we find that it is incapable of expressing adequately our experience of organic phenomena.

Let us now see where, in rough outline, the application of that conception to organic phenomena is inadequate. The most striking differential feature of living organisms is what may be called their active and specific stability. The bodies which we ordinarily meet with in the inorganic world possess a greater or less amount of stability; but this is interpreted as being of a passive kind, not dependent on continuously maintained activity within them. In the body of a living organism the stability of form and composition is evidently due, not to passive resistance to changes in the environment, but to continuous activity so coordinated that, though its material is constantly changing, the specific form and composition of the living body are on the whole maintained, or that if changes in these are in progress, as during development, these changes are on the whole of a definite and specific character in each species of organism. We give recognition to this fundamental fact when we say that the organism is alive, and belongs to a species. The reactions of a living organism to changes in what we interpret as its physical and chemical environment are so co-ordinated that the organism tends to be maintained, or else only to undergo such changes in character as are specific to it. A distinguishing characteristic of fundamentally the same kind is the capacity an organism possesses of reproducing itself in every detail, the reproduction starting in part of itself. The significance of the co-ordination for the theoretical interpretation of biological observation cannot be overstated. If we neglect it, we neglect all that is characteristic of biological phenomena; and any general discussion of life which ignores it is simply irrelevant.

We find that organisms are in constant active relations with their environment; but that this activity is on the whole so directed as to maintain in each organism a normal or specific condition, expressing itself as actively maintained structure and composition. In other words, the properties or mode of action on one another of the parts involved in the life of an organism, whether these parts are within or outside its body, not only depend on their active relations to one another, but these relations are specific or normal for each organism. Moreover, the normality of an organism is absolutely bound up with its surrounding environment. Regarded from a physical standpoint, this environment may seem to be variable and constantly changing; but when we examine more closely the immediate environment of what we may be led to regard as the essentially living parts of an organism we find that this immediate environment is actively maintained just as is the supposed living structure itself. We see this very clearly in the case of the blood-plasma and other internal media of higher organisms. In fact we cannot distinguish between normal living structure and its normal environment, and consequently cannot say where living structure ends and environment begins. We can thus discover no spatial demarcation between what is living and not living. Physiological investigation soon forces us to this conclusion. As regards the less immediate environment, the influence which it exerts on the body is normally determined, like that of any part of the body itself, in such a way that the normal structure and activity of the body tends to be maintained. Thus the external environment participates in the normality expressed in life, and is thus not something outside life. We cannot regard the external environment as outside of life.

The essential independence of what we interpret as “bodies” in the physical sense seems, therefore, to disappear in connexion with biological phenomena. The parts of the actively maintained whole which constitutes a unit of life do not exist independently of one another and their environment. They are not things which can be separated without essential change of properties, as appears to be the case with what we interpret as inorganic bodies. We study the details of their specific spatial relations to one another in morphology, and the details of their specific mutual influence in physiology; but since their form, structure, and composition are the outcome of constant activity, and this activity expresses itself in the form, and composition, it is only life itself that we are studying whether we approach it from the side of normal form and structure, or of normal activity, or of the chemical substances normal to organisms and their environment.

Let us now endeavour to regard to life from strictly physical standpoint. From this standpoint we must admit that living structure is nothing but an appearance, like that of a flowing stream, produced by a flow, or ebb and flow, of material. From physical standpoint we are obliged to assume that the flow is a flow of molecules, atoms, and electrons, entering into various combinations with one another in the course of the flow; and that there is a corresponding flow and transformation of energy. When we measure and analyse the intake and output to and from a living organism of what we interpret as matter and energy the results agree as exactly as could be expected with the physical interpretation. There is, from the observations, no suggestion whatever of any real failure in agreement. We can also follow to some extent what we interpret as matter and energy in its course through living organisms; and in so far as we can do so we are apparently helping to a physical and chemical account of life. A view which has been held by certain philosophers and theologians from the time of Democritus onwards, is that if we had sufficient data we should be able to furnish a complete physical and chemical account of life; and many biologists, particularly in the latter part of last century, have accepted this view, which has now become thoroughly popularized.

Such a view fails completely to give recognition to the co-ordination manifested in the actively maintained, and actively reproduced, structure and physiological environment of living organisms. The fact that living organisms maintain and reproduce themselves in spite of great variations in their physical and chemical environment is of course evident. In order to account mechanically for this fact it is necessary to suppose that their structure is so arranged, or in theological language “designed,” that it responds to changes in environment in such a way that, on the whole, the disturbing effects are annulled; that, for instance, effects which would otherwise be those of injury, disease, shortage of food or oxygen or water, or accumulation of waste products, are compensated for. We must thus assume an extremely complicated physico-chemical structure within the living body. In so far as we can discover such structure, the physico-chemical theory holds good; but if we stopped where such discoveries end, we should simply have ignored what is characteristic of life. It is not the mere reactions of a structure in the physical sense that we are dealing with, but the absolutely characteristic fact that specific structure and composition themselves are being constantly maintained and reproduced, as well as specific activity. To attribute the maintenance and origin of specific structure to specific structure itself is only to reason in an evident circle—to substitute mere words for ideas. It is impossible to maintain that the physical and chemical structure of a living organism accounts for its life.

We are thus forced to the conclusion that in the phenomena of life we are in presence of what cannot be interpreted physically, but implies a fundamental conception different from those of physical science. This conception is that of life, and biology is the science which uses the conception of life as its foundation. The widely spread popular belief that the physical and chemical structure of a living organism accounts for its specific behaviour is baseless.

In former times, when far less was definitely known about the metabolism of living organisms, their reproduction and embryology, and the evolution of species, the considerations to which I have just pointed did not assume their due weight. The structure of living organisms was either attributed to a supernatural act of creation in the past, or (as in the treatise De Formatione Foetus by Descartes) to causes now quite easily seen to be non-existent. With the advance of knowledge it has become more and more evident that unless we take refuge in what amounts to the theory of constant supernatural intervention within the body to help out the inadequacy of the physico-chemical theory of life, that theory is quite untenable.

Any theory implying so-called supernatural intervention is repugnant to science, since it implies the giving up of the endeavour, which is the inspiration of science and philosophy, to discover consistency and order. That any such theory, is, in the last resort, also inconsistent with religion, will be maintained in later lectures. If, however, we adhere to the view that the physical or physico-chemical conception of the visible and tangible world expresses its reality, we seem to be driven into the assumption of some sort of non-natural interference with this world in the case of living organisms. But even this assumption is precluded, since we can show experimentally that any supposed supernatural influence is dependent on influences emanating from the assumed physical environment.

Thus we cannot dispense with the specific conception of Life, and are hence compelled to regard the physical conception of the inorganic world as in ultimate analysis only provisional and superficial. The ordinary physical conception of the visible and tangible world was framed without taking into account the phenomena presented in living organisms, which are part of the visible and tangible world which we call Nature. It was a mere matter of practical convenience that this exception was made, and when this exception is made we have a conception of very great practical utlility in its own sphere. The actual world which we observe has all sorts of characteristics which were disregarded in framing the physical conception, and were set aside as belonging to what Locke called the “secondary qualities” of things, or to a supernatural world. The nemesis of the neglect of the organic meets us when we attempt to frame a physico-chemical biology. Our final conception of the visible and tangible world must cover organic as well as inorganic phenomena, and no general conception which falls short of this can be more than provisional.

On examining the framework of the ordinary conception of the inorganic world we find that “bodies” have been taken as things existing independently of their relations to one another, and of their activity and its specific character. They are thus different in kind from what the parts involved in life appear, on full examination, to be. If, however, we also regard the “bodies” of the inorganic world as existing in virtue only of their relations to one another and their specific activity, the gulf between the organic and the inorganic seems to be bridged. Chemistry has revealed to us the fact that visible bodies are aggregates of molecules or atoms; and until recently atoms were regarded as simply extremely minute bodies existing independently of their own activities and of other bodies. Not only, however, do we now know that atoms are compound bodies, but it appears that both the mass and specific properties of the electrons and protons of which they consist are inseparably bound up with their activity within the atom. This activity is specific in character and cannot be got rid of. If, moreover, it is increased or diminished, the changes only occur in specific steps.

The new conception of the atom, as revealed by the discovery of radio-activity, and the investigations of J. J. Thomson, Rutherford, Planck, Niels Bohr, and others, in conjunction with those of Einstein, bears striking resemblances to phenomena which biological investigation presents. But it is perhaps too early as yet to go further than point out that there is no need to assume in the case of life any ultimate inconsistency with what we call physical phenomena, however strongly we insist that the phenomena of life are inconsistent with the ordinary popular physico-chemical conception of visible and tangible reality which has come down to us from Galileo and Newton. It is reality with which all science, including biological science, ultimately deals, and not merely an idealized world, such as the world which, however usefully, Galileo and Newton represented to us appears now to be.

Bohr's conception of the atom, embodying as it also does the principle of relativity, implies a very radical recasting of the Newtonian conception of at any rate part of the physical world—apparently of the same nature, as the recasting which seems to be necessitated when we assume that life, with all its distinguishing characteristics, is simply a “natural” phenomenon. We know, as yet, but little about the genesis and disintegration of atoms, or how far these processes are comparable to the reproduction and death of organisms. Nor have we data for comparing organic with atomic variation. Nevertheless, on the new theory of the atom its form is specific, and the expression of specific activity, just as is apparently the case in a living organism; and since visible bodies are made up of atoms, and “cohere” in virtue of atomic properties, we are justified in assuming that behind all superficial appearances the inorganic world may in reality be constituted on principles similar to those which we seem to find exemplified when we study life. If so, the Newtonian conception, even if it were amended by introducing relativity into it, would no longer represent reality.

The fact that the principles of conservation of mass and of energy can ordinarily be verified so successfully is thus no proof that such separate entities as matter and energy exist or that in reality Nature obeys mechanical laws. In a universe of self-existent atoms or other minute units of mass to which self-existent energy had been unequally distributed, the inevitable tendency by the law of probabilities would be for the energy to become on an average equally distributed among the units, so that no sensibly evident part of this universe could do work on or influence any other sensibly evident part. This will no longer be the case, however, if the mass and energy are themselves the expression of an underlying reality which manifests itself in the variegated and specific forms of the observed physical world, corresponding to the variegated forms which life takes.

Enough has been said to indicate that in rejecting mechanical conceptions of life, and interpreting it in the manner which is directly required by the observation of life itself, we are not necessarily assuming the evistence of any supernatural factor, or of anything different in kind from what can possibly be found in the so-called inorganic world when it is examined sufficiently closely. In the case of what we call organic phenomena we can see from the outset that mechanical interpretations are impossible. In the case of what we call inorganic phenomena, on the other hand, we can at present see only by dint of careful quantitative experiments that mechanical interpretations are ultimately not sufficient, though in ordinary cases mechanical interpretations are extremely useful and trustworthy for purposes of prediction, and can be applied without difficulty.

The conception of reality or Nature to which we are directly led by the study of life is very different from that to which, except on very exact and deep study, the isolated consideration of what we distinguish as inorganic phenomena leads us. For this reason biology must, it seems to me, be regarded for the present as an independent science, guided by a conception different from the mechanical conception which is ordinarily satisfactory in the physical sciences. In the next four lectures I propose to deal with the attempts which have been made, either to interpret life on ordinary physical and chemical assumptions alone, or to interpret it on these assumptions with the help of the assumption that living organisms are the seat of what may broadly be called supernatural influences.

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  Die organische Chemie in ihrem Zusammenhange mit dem Stoffwechsel, 1845.