The organic unity displayed in the immediate environment of a living organism is evident enough, and becomes more and more evident as biological investigation is extended. This is not only the case as regards the blood, which may be designated, after Claude Bernard, as the internal environment of higher animals, but also as regards the immediate environment in a wider sense, including the alveolar air, intestinal contents, and usually also the temperature, moisture, and movement of the air in immediate contact with the skin. When, however, we consider the environment in a wider sense, we are apt to think that the conception of organic unity cannot be extended to it.
An organism is physiologically connected with the wider environment through its skin, organs of sense, or in the case of lower organisms and plants through receptive structures of various kinds. In the case of plants, for instance, the combined influence of light and the surrounding atmosphere is largely through chlorophyll-containing cells beneath the epidermis, which itself, with the aid of stomata, controls the influence of the surrounding atmosphere.
Let us consider the connexion between a higher organism and its wider environment through its skin and sense-organs. We can endeavour to regard this connexion from a mere physical standpoint, just as we can consider respiration, circulation, or digestion from this standpoint. From the physical standpoint impressions are constantly being produced on the skin and sense-organs, and may be transmitted in a reinforced state along afferent nerves or through the blood to the central nervous system. Here they may spread, with further reinforcement, until they reach nerve-cells connected by efferent nerve-fibres with muscles and other organs of which the activity is aroused or inhibited by them, this being the final response of the body to afferent impressions.
It is of considerable practical service to be able to interpret the connexions in this way, and to follow out all the details of the connexion. There is, however, no direct biological interest in such interpretation, and its inadequacy is evident at once. As soon as we enquire further into the connexion it becomes evident that not only the impressions on the sense-organs, but also the whole train of further consequences, are co-ordinated in a manner of which the physical interpretation has given no account. In the case of conscious responses there are, in addition, all the characteristic features of perception and conscious response, to which the physical interpretation gives us not the smallest clue. Consciousness, may, however, be entirely absent, so far as can be ascertained, and it is only the purely biological aspect of what is happening that will be considered in this lecture.
The biological connexion between organism and environment through the sense-organs and skin can be studied quite easily in man by observing sensory activities of which we are conscious, and at the same time deliberately leaving out of account their psychological aspects as perceptions of a surrounding world. In other words, we can study them simply as physiological activities, or as physiology of the senses, just as we study unconscious activities of respiration, nutrition, excretion, or circulation.
The first point to be made in connexion with sensory activities is the constancy of their influence. At first sight it might seem that when the surface of the body, or the fields of vision, hearing, smell, or taste, are not specially excited by some external disturbance, there is no sensory or afferent influence in the corresponding fields. That this view is a mistaken one becomes evident when we reflect that the particular character of efferent activity depends at all times not merely on special isolated afferent stimuli, but also on many other simultaneous afferent influences. The particular sort of movement evoked in a limb by an external disturbance or “stimulus” depends on innumerable afferent exciting or inhibitory influences corresponding to the position of the limb at the moment and that of the whole body, together with all the chemical or so-called metabolic influences which determine the strengths of afferent impulses. A living organism does not behave like a machine which when some particular stop is pressed or handle turned responds always in some particular manner. The manner depends on an indefinite number of other stops, constantly in variable operation and reacting on one another in an indefinite number of different ways. From a physical standpoint, therefore, the response of the living organism to external disturbance depends upon endless circumstances. The simple general conception, which Descartes illustrated in his De Homine, of reflex responses does not at all correspond with observation.
Throughout all this endless complexity the one thing which appears as a net outcome is that the life of the organism is maintained or fulfilled in a characteristic manner. This is an elementary fact of observation, just as from the physical standpoint the existences of mass and energy seem to us to be elementary facts. In other words, we perceive that the connexion between an organism and its external environment is a living connexion in virtue of which specific living structure is maintained through specific activity, so that we can designate the connexion as the life characteristic of a species, and investigate its details from this point of view, which is that of biology.
From a physical standpoint the maintenance of the specific structure of a living organism in presence of a constantly and chaotically changing external environment would appear as a continuous miracle demonstrating the presence of some sort of supernatural intervention. From the biological standpoint life is just a manifestation of Nature, and it is no mere miracle or inconceivably improbable coincidence of physical events that an organism nourishes itself, reproduces itself, and maintains its specific structure and activities. The environment is thus not something foreign to it, but enters into its own life. What influences its receptive organs and structures influences them as participating in the unity of its own life, so that this life extends indefinitely beyond the confines of the body. To a biologist the external environment of an organism enters just as much into its life as the parts of its own body or the internal environment. Through the organs of sense and other receptive organs the surrounding external environment participates in its whole life, and biology interprets this participation.
From a physical standpoint material and energy are constantly or at intervals entering the body of a living organism, and afterwards leaving it; and we can balance the intake of both material and energy against the output if nothing is left in or taken from the body. The balance is always true, leaving no demonstrable margin corresponding to any other appearance or disappearance of either material or energy. On the other hand, however, the intake and output of both material and energy are subject to constant physiological co-ordination. This means no less than that the influence of the environment on the organism, and of the organism on the environment, express the maintenance of specific normal structure and activity. Of this there is not only no physico-chemical explanation any more than there is for the maintenance of structure and activity within the body, but, just as between the parts of the body, the relation also between the body and its environment expresses the maintenance of what is normal.
Wherever physiology is concerned, as in the general physiology of nutrition, with the relations between organism and environment, it is the maintenance of normal conditions and the manner in which that maintenance is brought about that are of interest. Our knowledge of what these normal conditions are, and how they are maintained, is constantly growing; but the conception of normal conditions and their maintenance is fundamental, whether we are considering the phenomena of life within the body or its relations to environment. In biology we never get away from the specific conception of life, and the attempt at a mere physico-chemical account of the relations between organism and environment misses the relevant facts and leaves us in a chaotic maze of quite unintelligible causal connexions. If we take the fashionable word “bio-chemistry” in its literal sense, and set out to give a purely chemical account of the phenomena of nutrition, we lose ourselves inevitably in this maze. My work as a physiologist has been almost entirely on the chemical side, and I am speaking from wide experience, though no one realizes better than I do how useful the word “bio-chemistry” has been in obtaining much-needed endowments.
Let us now consider the general characters of the physiology of vision. Through vision a living organism is kept in active connexion with its environment in all directions up to indefinite distances. The field of vision, however rudimentary may be the organs of vision, brings the body into an oriented relationship with the whole of a biologically co-ordinated environment simultaneously, just as the tactile field does. This relationship is preserved in higher organisms through the mobility of the eyes and head and the presence of the crystalline lens, which projects on the retina an image of the environment. For the individual organism space-arrangement is its own individual space-arrangement, centred in, or relative to, itself, and thus essentially relative.
Visual orientation is closely co-ordinated with tactile, heat-sense, auditory, gustatory, and olfactory orientation; and though visual, auditory, and olfactory activity may not coincide with tactile activity, the combined field of co-ordinated sense-activity is solid. When we consider the nature of the oriented connexion through sense-activity, the biological connexion shows itself to be different from mechanical connexion, for we cannot separately distinguish influences of one sort from other influences. The influences of different parts of the visual field do not appear and disappear in the same manner as in mechanical action, though varying in action from moment to moment. They also persist as a whole, and in specific interconnexions with one another, just as the specifically co-ordinated activities within the bodies of living organisms persist actively. We find that the activity of one part of the field of vision is bound up with the activity of other parts, and thus depends on what we call contrast. As activity increases in one part of the field it automatically diminishes in other parts; but in the field as a whole it tends to remain constant. Weber's law of sensation, according to which the degree of excitation in any part of the field depends, not on the exciting influences as measured physically, but on their relation to simultaneous other excitations in the field, is of fundamental biological significance.
If, as in photometry, we wish to measure physical differences in strength of light-excitation, we can do so accurately if we keep the surrounding field even in its influence, as when, in comparing two illuminations, the whole of the rest of the field of vision is either darkened or evenly illuminated round the two illuminated surfaces which are being compared. If the surrounding illumination is uneven, the comparative measurement is more or less falsified; and this is particularly evident in comparing tints of colour, as we find at once on transposing the tinted surfaces. A painter represents depths and tints of illumination as they appear physiologically, and not as a physicist might measure them. In this respect the painter, like the physiologist, neglects completely the “physical reality” of intensity and predominant wavelength of radiation. To painter and physiologist alike, what is bright or coloured in a definite manner depends on the surrounding depths and tints of illumination. It is only through confusion of mind that we identify brightness and color with intensity and wave-lengths of physical illumination.
As regards the delicacy of visual excitation, it is well known, for instance, that within enormously wide variations of general illumination in the physical sense, the apparent brightness and the visibility of objects remain about the same. The physical illumination may be a thousand times greater with bright daylight than by the light of a candle at a distance of one or two feet; but objects seem to us about equally bright and visible with either illumination. It is only when we go to extraordinarily low illuminations in the physical sense, particularly when, as in a coal-mine, very little light is reflected by the illuminated surfaces, that objects become indistinguishable. Even when they are at first almost indistinguishable, as when a coal-miner, with only the illumination given by one of the very inadequate flame or electric safety hand-lamps still ordinarily used in this country, goes from daylight to the pit-bottom, the eye soon adapts itself so far to the dim illumination that surrounding objects become fairly visible.
When surrounding objects become invisible, this is not because visual excitation is absent, but because excitation produced in another way than by what we regard as external causes becomes so strong as to obscure the latter excitation, if a source for it is still present. In a room which is perfectly dark, the field of vision is not black but on the whole grey, though variegated and full of movement. It is not nothing that we see, but only nothing “objective.”
It is the same with the fields of our other senses. They are never empty in a physiological sense; and this is shown by the fact that the condition at any time of one field influences in a definite manner the responses to stimuli in other fields. In the dark we automatically proceed warily; and the absence of some particular set of afferent stimuli, such as those accompanying contact of the foot with the ground, may automatically stop or completely alter muscular movement.
It is quite impossible to interpret the actual relations between a living organism and its spatial environment as a mere relation between the self-existent “bodies” of Newtonian physics. The influences of the physical bodies cannot be distinguished separately. A living organism does not respond to objective reality as interpreted physically. The physical or physico-chemical influence appears to be distorted or altered to an indefinite extent. The assumed “primary” physical characters of the environment are overwhelmed by “secondary” characters which seem, from the physical standpoint, to be conferred on the environment by the organism. The physiology of the senses investigates these “secondary” qualities scientifically. This and other parts of the physiology of the nervous system are often confused with psychology.
When we examine these secondary characters, we find that to a constantly increasing extent we can interpret them biologically as corresponding to the physiological requirements for maintenance of life when the life of the organism is regarded as an actively and specifically maintained whole, including within itself the active relations between organism and environment. What seem from a physical or chemical standpoint to be mysterious variations in excitability, “tropisms,” etc., become intelligible biologically. The more we study them, the more and more intelligible do they become biologically, and the less and less intelligible physically. In this respect they are on exactly the same footing as the phenomena of respiration, circulation, absorption, excretion, etc., as discussed in the previous lecture.
The mechanistic school of physiologists assumed, and still assume, that it is not legitimate to interpret phenomena biologically in the sense which I have just indicated. For them visible and tangible reality is physical reality in the sense to which Newton gave clear definition, and there is no other visible or tangible reality unless it be something supernatural or else, perhaps, occurring in conjunction with consciousness within the body of an organism. To speak of distinctively biological interpretation of the environment thus implies “teleology” worthy of only the scholastics or of persons who do not make use of the common sense which is constantly confirming the Newtonian conception. Since the days of Francis Bacon, Galileo, and Newton, “teleological” interpretations of our external environment have been out of fashion, and the vitalists were in complete agreement with the mechanistic physiologists on this point.
On the mechanistic interpretation the apparent “teleological” relations between organism and environment are only apparent. Though organisms live through their reactions with their environment, this is only because their structure has peculiar characters which bring this about. According to theologians, this structure was given them in the remote past by a supernatural Creator. According to mechanistic biologists, the structure was acquired in the course of long ages, and became a dominant feature, specifically characterized for each species, through the influence of natural selection. The assumption of existing specific physico-chemical structure in the bodies of each species of living organism is thus an essential part of the mechanistic theory. Considering the amazing definiteness and complexity in the reactions of known living organisms, with their environment, and between different parts of their own bodies, the structure must be almost inconceivably complex. Nevertheless the mechanistic conception, whether theological or materialistic, seems a possible one so far. Let us follow it out farther, however.
Quite clearly, the mechanistic interpretation assumes the fact of hereditary transmission, and apart from hereditary transmission the theory of natural selection or of supernatural creation in the remote past would be meaningless. But what do we assume when we assume hereditary transmission? On the mechanistic interpretation, hereditary transmission means the reproduction in offspring of an enormously complicated physico-chemical structure. We must sweep away the crude idea that what happens is simply the increase and division of an albuminous substance without definite structure, called protoplasm. The substance must, on the mechanistic interpretation, be enormously complex and yet perfectly definite in molecular structure. But if it is so complex, how can we imagine its dividing into two parts, one at least of which must have the capacity of repeating the process indefinitely often?
A mechanist of robust faith would reply that though we do not understand the process, there must be some molecular mechanism by which the reproduction is brought about. In accordance with his robust faith he will also speak of the “mechanism” of reproduction. But the more we ponder over this question the more clearly it appears that the idea of a complex mechanism which can also reproduce itself or mend itself is not a coherent idea at all. In fact no scholastic absurdity was ever more of an absurdity than a mechanism of heredity. Those who may still have a lingering affection for a mechanistic conception of life, or who imagine that life must be something which had a beginning in time, would do well to ponder further over the nature of hereditary transmission. A mechanism of hereditary transmission is simply a contradiction in terms.
The reason why organism and environment are complementary to one another in such a way that life maintains itself cannot, therefore, be simply that the physico-chemical structure of any living organism is such as to promote this maintenance. It is quite true that what appears to us as mechanical structure and arrangement in the bodies of living organisms is always admirably fitted to promote their particular mode of life, whether they may be amoebae, elephants, oak trees, or human beings. Their structure and biological environment suit one another. But if, as I have argued, the life which manifests itself in a living organism is an actively maintained whole without spatial boundaries, both the structure and the life-activities of the organism must be manifestations of this organic unity, so that they fit one another in the manner found to be actually the case.
Heredity, the way in which a living organism is constantly renewing or replacing its structure, and the fact that structure is suitable to environment, are alike manifestations of life. They are not matters which either require or are susceptible of explanation in physical terms. In other words, they are just Nature—what is. We can observe and investigate their details as manifestations of life; and this is what biology actually does, with signal scientific success and practical advantage. To ask for a physical explanation of them is only blind foolishness.
Thus the conception of life as a specific co-ordinated unity of structure and activity applies indefinitely beyond the immediate environment of any living organism, and can be confined neither to anything within its body that might be distinguished as being specifically alive, nor to within the more immediate environment. The biological interpretation is, in fact, different from the physical interpretation but applies over the same phenomena; and by no possibility can we reduce biological to physical interpretation on the lines laid down by Galileo and Newton. However far we pass outwards from a centre of life, the biological interpretation is still there.
Just as within the bodies of living organisms we find scope for the application of both a biological and physical interpretation, so do we in their environment. We cannot consistently express in physical terms the observations which we interpret biologically. Nor do we see any way clear to expressing biologically the details which we interpret physically. But in view of the irreducibility of biological to physical interpretation, the only possibility of reaching consistency as regards interpretation of the two sets of observations would be by extending the biological interpretation to the observations interpreted physically. It is only, however, by an act of faith that we can do so. We cannot actually perceive life in the details of what we at the same time interpret as an inorganic world.
This faith is no mere groundless belief, but is based on the postulate, which is that of all knowledge or science, that our experience is ultimately consistent with itself. The mechanical interpretation of our experience is certainly inconsistent with biological observation; but in the growth of biological knowledge we see the continuous extension of biological interpretation to what we at first could only refer to in physical terms. There is no limit to the possibility of further extension in this direction in the future. On the other hand, there is no possibility of interpreting biological observations physically. We can, it is true, very often apply new physical interpretations to phenomena within and around living organisms; but just in proportion as we do so we find that we are also in presence of extended biological interpretation, so that biological interpretation has increased in the manner so strikingly exemplified, as already pointed out, in the history of physiology.
To put the same conclusions in a different manner, physical interpretation is of a more abstract character than biological interpretation. In physical interpretation, that is to say, we are leaving out of account essential features which must be present, though we cannot perceive them, and which are actually taken into account in biological interpretation. Just as physical interpretation takes into account features in our experience which are not taken into account by purely mathematical science, so does biological interpretation take into account features which are not taken into account in merely physical interpretation. For this reason we get nearer to reality in biological interpretation, and we are dealing to a less extent with mere abstractions, however useful in certain practical applications these abstractions may be, just as are the still greater abstractions of mathematical science.
I have dealt in this lecture with the external environment of living organisms because even when it is clearly seen that within the living bodies of organisms merely physical and chemical conceptions are inadequate scientifically, it is often supposed that in the external environment nothing but physical and chemical interpretation is required, and that we are surrounded by an environment in which mechanical chaos reigns supreme. This is even regarded as nothing but common sense.
I wish to emphasize as strongly as I can that the belief in a merely physical world surrounding us has no basis. Our environment is not something indifferent to our lives, but belongs to them. Surrounding Nature is not an influence outside our lives, but within them. From the standpoint of biology, Nature is not merely a healing and beneficent influence within the living body, as Hippocrates first clearly pointed out and every educated doctor takes as axiomatic, but is a healing and beneficent influence in the whole of our environment to the farthest depths of space. The supposed common-sense view to the contrary is only the common ignorance characteristic of the particular times in which we live. The facts of biology were left out of account in the scientific reasoning from which that view originated.
Had they been taken into account effectively, it would have been impossible to represent visible reality, as Newton did, as corresponding simply to the physical representation of it. But in Newton's time life was regarded from either the vitalistic or mechanistic standpoint, and this state of matters has continued up to the present time. In my book Mechanism, Life, and Personality, published first in 1913, I pointed out the impossibility of either the mechanistic or vitalistic conception of life. But nothing is more difficult than to persuade people to think, and to judge from various recent references to my opinions, I am commonly set down as a vitalist, or perhaps as a “neo-vitalist.”
The world has been familiar for long with mechanistic and vitalistic conceptions of life. As neither of these conceptions is satisfactory, it is surely time to do a little thinking on the subject of life. In this connexion I was particularly pleased to see, in the Presidential Address given by Professor Lovatt Evans to the Physiological Section at the recent (1928) meeting of the British Association in Glasgow, that he has reached conclusions essentially similar to my own.
At the same meeting the mechanistic view of life was presented in a popular lecture by Professor Donnan. Needless to say I regard this view as now entirely obsolete, since it ignores the observed facts; and this is far more evident now than it was a few years ago, before physiology had become to so large an extent a quantitative science. The fact that Professor Donnan, though his work in physical chemistry commands universal respect among those who know it, is not a physiologist, may partly account for his opinions.