ORGANISMS AND MACHINES;
and while on the one hand the legitimate striving of the biologist to display the mechanism of organic actions has been denounced by a certain school as Materialism and a hateful attempt to “rob Life of its mystery,” there has been on the other hand a misconception of this mechanism, as if its dependent actions were of the nature of machines, that is to say, as if organized mechanisms were strictly comparable with machines constructed of inorganic parts. No doubt the laws of Mechanics are the same in both, for these are abstract laws which take no account of concrete differences. But when elaborate parallels are drawn up between steam-engines and animal organisms, the coal consumed in the one likened to the food in the other, and the force evolved in the combustion in both being the same, there is a complete obliteration of all that specially distinguishes vital activity.
79. Between an organism and a machine there is the superficial resemblance that both have a complex structure, and are constructed of different and dependent parts. But underneath this resemblance there is a radical diversity.[32] The arrangement of parts in the organism is more than a juxtaposition, it is a solidarity, arising from the fact of their being all differentiations from a common substance which is a special combination of the three classes of proximate principles. Thus they are not parts which have been put together, but which have been evolved, each out of a pre-existing part, and each co-operating in the very existence of the other. The machine is made of independent and primarily unrelated parts; its integrity depends on the continued preservation of the substance of each part; waste is here destruction. The organism is constituted by interdependent and primarily related parts; its integrity depends on the continued destruction and renovation of their substance; waste is a condition of vitality. The actions of the machine are subordinated; the actions of an organism are co-ordinated. The lever moves a wheel, and the wheel in moving liberates a spring, each transmitting a communicated impulse, but otherwise each acts independently—no slight modification in the structure or movement of the wheel will modify the structure or the movements of the lever, no alteration in the tension of the spring will affect the structure of the wheel. But in the organism all are parts of one sympathetic whole; each reacts on each; each is altered by the other. Not a nerve is stimulated, nor a muscle moved, but the entire organism is affected. A condensation here is the cause of a greater imbibition there. The injection of salt or sugar under the skin of the frog’s leg will produce cataract in its eye. The activity of a secreting cell in the ovary, or liver, alters the condition of the brain; the activity of the brain will check the secretion of a gland, or relax the sphincters of the bladder. When we observe the growth of horns, or the appearance of the beard, concomitant with the secretion of spermatic cells—and especially when we observe with these a surprising change in the physical and moral capabilities and tendencies of the organism—we understand how the remotest parts of this mechanism are bound together by one subtle yet all-powerful tie. Nothing of this is visible in a machine. In a machine the material is so far of secondary importance that it may be replaced by materials of various kinds: a pulley may be worked with a hempen cord, a silken cord, or an iron chain; a wheel may be wood, iron, copper, brass, or steel; the actions will in each case be similar. Not so the organic mechanism: the slightest variation, either in composition or intimate structure, will affect, and may frustrate the organic activity. It is only in the skeleton that the specific character of the materials may be changed; and here only in the substitution of one phosphate for another in the solid masonry.[33]
80. Another marked characteristic of the organism is that it has a connexus of actions, the simultaneous effect of a continuous evolution, appearing in stages and ages. And in the animal organism there is a consensus as well as a connexus, through which there is evolution of Mind; and in the Social Organism an evolution of Civilization. This consensus forms an intermediate stage through which the animal actions are sensitive as well as nutritive, and the nutritive are regulated by the sensitive. It is obvious that nothing like this is to be found in a machine; and we conclude, therefore, that any view of the organism which regards its mechanism without taking in these cardinal characteristics must be radically defective. We no more deny the existence of mechanical phenomena in denying that the organism is like a machine, than we deny the existence of chemical phenomena in denying that Vitality is chemical.
CHAPTER IV.
THE PROPERTIES AND FUNCTIONS.
81. The terms Property and Function are not always used with desirable precision. There is, however, a marked distinction between the property which characterizes a tissue in whatever organ the tissue may be found, and the function which is exhibited by an organ composed of several tissues. We ought never to speak of a function unless we imply the existence of a correlative organ; and it is therefore incorrect to speak of the function of Nutrition, since all the tissues nourish themselves; but we may speak of certain organs as special instruments in facilitating Nutrition. Thus also with respiration, usually, but not accurately, spoken of as the function of the lungs; the lungs being simply the most effective of the instruments by which the interchange of gases (which also takes place in every tissue) is facilitated. If by Respiration we mean Breathing, then, indeed, Respiration is the function of the lungs; if we mean the absorption of oxygen and the exhalation of carbonic acid, Respiration is a general property of vital tissue. A fragment of muscle removed from the body respires, so long as its organization is intact; but it does not breathe—it has no accessory instruments, nor does it need them. The co-operation of nerve centres, diaphragm, ribs, circulating system, etc., necessary in the complex organism to bring the due amount of oxygen to the tissues, and convey away the carbonic acid, is here needless. In the ascending animal series we find this necessity growing with the complexity of the organism. The whole skin respires in the amphibia, and to some extent in man also: a frog will live for ten or fourteen days after extirpation of its lungs, the skin respiring sufficiently to keep up a feeble vitality. But the skin does not suffice; and, very early, certain portions are specialized into organs (at first in the shape of external gills, and finally as internal lungs), for the more energetic, because more specialized, performance of this office. In the simpler organisms the blood is easily reached by the air; therefore no instrument is needed. In primitive societies the transport of goods is effected by men and women carrying them; in civilized societies by the aid of horses and camels, and wagons drawn by oxen; till finally these are insufficient, and railways are created, whose power of transport transcends the earlier methods, as the breathing of a mammal transcends the respiration of a mollusc. Breathing is the special function of an organ—the lungs (or more strictly, the thoracic apparatus)—as Railway Transport is a special social function. Although each of the tissues forming this organ can, and does, exhale carbonic acid and absorb oxygen—and each of the railway servants can, and does, transport objects to and from the locomotive—yet the main work is thrown upon the special apparatus.
82. What is meant by properties of tissue and functions of organs may be thus illustrated. Let us suppose ourselves investigating the structure of a ship. We find it composed of various materials—wood, iron, copper, hemp, canvas, etc.; and these under various configurations are formed into particular parts serving particular purposes, such as deck, masts, anchor, windlass, chains, ropes, sails, etc. In all these parts the materials preserve their properties; and wherever wood or iron may be placed, whatever purpose the part may serve, the properties of wood and iron are unaffected; and it is through a combination of these properties that the part is effective; while through the connection of one part with another the purpose becomes realized. The purposes to which masts, ropes, or sails are subservient may be called their functions; and these of course only exist, as such, in the ship. It is the same with the organism. We find it composed of various Tissues, and these are combined into various Organs or Instruments.[34] The properties of Tissues remain the same, no matter into what Organs they may be combined; they preserve and exert their physical, chemical, and vital properties, as wood and iron preserve their properties. Each Tissue has its characteristic quality; and the Organ which is constructed out of a combination of several Tissues, more or less modified, is effective solely in virtue of these properties,[35] while the Function of that organ comes into play through its combination with other organs. For example, muscular tissue has a vital property which is characteristic of it, Contractility; and muscles are organs constituted by this tissue and several others;[36] such organs have the general function of Contraction, but whether this shall be specially manifested in the beating of the heart, the winking of the eyelid, the movement of the chest, or the varied movements of the limbs, will depend on the anatomical connections. The reader unfamiliar with Biology is requested to pay very particular attention to this point; he will find many obscurities dissipated if he once lays hold of the “principal connections.”
82a. Although Bichat’s conception was of great value, it was not sufficiently disengaged from the metaphysical mode of viewing biological phenomena. Both he and his disciples will be found treating Properties as entities, and invoking them as causes of the phenomena instead of recognizing them simply as abstract expressions of the phenomena. Readers of my First Series will remember how often I have had occasion to point out this common error: men having baptized observed facts with a comprehensive name, forget the process of baptism, and suppose the name to represent a mysterious agency. The fact that gases combine is expressed in the term affinity; and then Affinity is understood to be the cause of the combinations. The fact that bodies tend towards each other is called their gravitation, and Gravitation is then said to cause the tendency. The doctrine of vital properties has been thus misunderstood. While no one imagines that he can operate on affinity otherwise than by operating on the known conditions under which gases combine, many a biologist and physician speaks as if he could operate on the Irritability of a tissue, or the Co-ordination of muscles, by direct action on these abstractions.
Let it be therefore once for all expressly stated that by the property of a tissue is simply meant the constant mode of reaction of that tissue under definite conditions. The property is not a cause, otherwise than the conditions it expresses are a cause. And these conditions are first those of the organized structure itself, and secondly those of the medium in which it lives. Oxygen unites with Hydrogen to form water, but only under certain pressures; so likewise muscles manifest Contractility on being stimulated (that is their mode of reaction), but only under certain degrees of temperature, humidity, and a certain chemical composition of the plasmode. The property is so truly an expression of the co-operant conditions, that it is found to vary with those conditions, and to vanish when they vary beyond a certain limit.
An attempt has been made to restrict the notion of a property to an ultimate fact. Whatever is not reducible to known conditions is to be accepted as a property. Combustion, for example, is reducible to the molecular combination of oxygen and some other gas; but this combination itself is not reducible, and it is therefore christened affinity. I cannot accept this view. Admitting our inability to say why gases combine under certain conditions (and in this sense all facts are inexplicable and ultimate, unless we take the how as ample explanation of the why), I must still say that since affinity itself depends on the co-operation of known conditions, it is not less explicable than combustion. But the point is unimportant: what we have here to settle is the meaning of a property of tissue,—and that is the mode of reaction which that tissue manifests under constant conditions, internal and external.
83. The evolution of Life is the evolution of special properties and functions from general properties and functions. The organism rises in power as it ramifies into variety. Out of a seemingly structureless germinal membrane, by successive differentiations certain portions are set apart for the dominant, or exclusive, performance of certain processes; just as in the social organism there is a setting apart of certain classes of men for the dominant or exclusive performance of offices, which by their co-operation constitute Society. The soldier fights, but ceases to build or reap, weave or teach; the mason builds; the agriculturist sows and reaps; the priest and thinker teach; the statesman governs. In simple societies each does all, or nearly all; but the social life thus manifested is markedly inferior to the energetic life of a complex society. So with organisms. An amœba manifests the general properties of Nutrition, Reproduction, Sensibility, and Movement. But it has no special organs, consequently no special functions. The polype has a certain rudimentary specialization of parts: it has a simple alimentary cavity, and prehensile tentacles; and although by these it can seize and digest its prey, it can only do so in a limited way—all the manifold varieties and power of prehension and digestion observed in more complex organisms are impossible with such organs as the polype possesses.
84. Differences of structure and connection necessarily bring about corresponding differences in Function, since Function is the directed energy of the Properties of tissues. One organ will differ from another in structure, as the liver from the pancreas, or the kidney from the spleen; or one organ may closely resemble another but differ from it only in connections, as a sensory and a motor nerve, or an extensor and a flexor muscle. We must therefore always bear both points in mind. Every modification, structural or connectional, is translated by a corresponding modification in the office. The hand and the foot show this well. The tissues are the same in both, the properties are the same, and both have the same general function of Prehension; but their morphological differences carry corresponding differences in their uses.
Suppose we have a galvanic battery, we know that its electric force may be variously applied. Two pieces of charcoal fixed to the ends of its conducting wires give us the electric light; replacing the charcoal by a telegraphic apparatus we can transmit a message from one continent to the other; the wires dipped in a solution effect a chemical decomposition, dipped into a mixture of gases they effect a chemical composition. In these, and many other applications, the property of the battery is constant; but the functions it subserves have varied with the varying co-operants. So with the properties of tissue.[37] Not only have we to bear in mind the organic connections of the tissues, but also the relation of the organs to their media. Swimming and Walking, for example, are both functions of the locomotive apparatus, but they are specially differenced by the media in which the animal moves.
85. The properties of tissues are their peculiar modes of reaction, and each tissue has its dominant characteristic, such as the Contractility of the muscle, and the Neurility of the nerve. But there has of late years sprung up a misleading conception, partly a consequence of the cell-theory, and partly of the almost inevitable tendency of analysis to disregard whatever elements it provisionally sets aside; this conception is the removal of the property from its tissue, and the localization of it in one of the organites—cell or fibre. This has been conspicuously mischievous in the case of the nerve-cell, which has been endowed with mysterious powers, and may be said to have usurped the place of nerve-tissue. I shall have to speak of this in the next problem. Here I only warn the student against the common error. The properties of a tissue depend on the structure and composition of that tissue, together with its plasmode and products; they vary as these vary. To select any one element in this complex, and ascribe the reaction of the tissue to that, is only permissible as a shorthand expression.
86. What has just been expounded may be condensed in the following biological law:—
Identity of tissue everywhere implies identity of property; and similarity of tissue corresponding similarity of property. Identity of organic connection everywhere implies identity of function; and similarity of organic connection similarity of function.
87. This law, first formulated by me in 1859, and then applied to the interpretation of nervous functions, was so little understood that for the most part it met with either decided denial or silent neglect; no doubt because of the general disinclination to admit that the properties and functions of the spinal cord could be similar to those of the brain, in correspondence with the similarity of their tissues and organic connections. Even Professor Vulpian, who adopted it, as well as my principal interpretations, hesitated, and relapsed into the orthodox view in assigning three different properties to one and the same tissue in cord, medulla oblongata, and cerebrum.[38] In the course of our inquiries we shall so frequently have to invoke this law that I earnestly beg the reader to meditate upon it, and ask himself upon what other grounds, save those of structure and connection, the properties and functions can possibly rest? If on no other, then similarity in structure and connection by logical necessity involves similarity in property and function.