40 THE DATA OF BIOLOGY.
body, than it is out of the body.* Thus, to carry further the simile used above, the atoms of hydro- carbons and oxy-hydro- carbons contained in the tissues, are, like bricks on end, not in the stablest equilibrium, but still in an equilibrium so stable, that they cannot be overthrown by the chemical and thermal forces which the body brings to bear on them. On the other hand, being like similarly-placed bricks that have very nar- row ends, the nitrogenous atoms contained in the tissues are in so unstable an equilibrium that they cannot withstand these forces. And when these delicately-poised nitrogenous atoms fall into stable arrangements, they give impuls3s to the more firmly-poised non-nitrogenous atoms, which cause them also to fall into stable arrangements. It is a curious and significant fact, that in the arts, we not only utilize this same ^ principle of initiating extensive changes among comparatively stable compounds, by the help of com- pounds much less stable; but we employ for the purpose compounds of the same general class. Our modern method of firing a gun, is to place in close proximity with the gun- powder which we wish to decompose or explode, a small por- tion of fulminating powder, which is decomposed or exploded with extreme facility; and which, on decomposing, communi- cates the consequent molecular disturbance to the less-easily decomposed gunpowder. When we ask what this fulminating powder is composed of, we find that it is a nitrogenous salt.
Thus various evidences point to the conclusion, that besides the molecular re-arrangements produced in organic matter by direct chemical action, there are others of kindred importance produced by indirect chemical action. Indeed, the inference * May it not be well to inquire wlipthev alcohol is not, in a greater or loss measure, transformed in the body into acetic acid? If, when in contact with changing nitrogenous matter, in presence of oxygen, alcohol undergoes this transformation out of the body, it seems not improbable that it does so in the body —especially as the raised temperature which aids the change in the one case exists in the other. It would be out of place here to set down the sundry facts which countenance this hypothesis. I may say, however, that it apparently removes some of the difficulties which at present perplex the question.
. THE ACTIONS OF FORCES ON ORGANIC MATTER. 41 that some of tlie leading transformations occurring in the animal organism, are due to this so-called catalysis, appears necessitated by the general aspect of the facts; apart from any such detailed interpretations as the foregoing. We know- that various amylaceous and saccharine matters taken as food, are decomposed in their course through the body. We know that these matters do not become components of the tissues, but only of the fluids circulating through them; and that thus their metamorphosis is not an immediate result of tho organic activities. We know that their stability is such that the thermal and chemical forces to which they are exposed in the body, cannot alone decompose them. The only explan- ation open to us, therefore, is that the transformation of these oxy-hydro- carbons, into carbonic acid and water, is due to communicated chemical action.
§ 16. This chapter will have served its purpose if it has given a conception of the extreme modifiability of organic matter by surrounding agencies. Even did space permit, it would be needless to describe in detail the immensely varied and complicated changes which the forces from mo- ment to moment acting on them, work in living bodies. Dealing with biology in its general principles, it concerns us only to notice how specially sensitive are the substances of which organisms are built up, to the varied influences that act upon organisms. And their special sensitiveness has been made sufiiciently manifest, in the several foregoing sections.
CHAPTER III.
THE RE-ACTIONS OF ORGANIC MATTER ON FORCES.
§ IT. Be-distributions of Matter, imply concomitant re- distributions of Motion. That which under one of its aspects we contemplate as an alteration of arrangement among the parts of a body, is, under a correlative aspect, an alteration of arrangement among certain momenta whereby these parts are impelled to their new positions. At the same time that a force, acting differently on the different units of an aggre- gate, changes their relations to each other; these units, re- acting differently on the different parts of the force, work equivalent changes in the relations of these to one another. Inseparably connected as they are, these two orders of phe- nomena are liable to be confounded together. It is very needful, however, to distinguish between them. In the last chapter, we took a rapid survey of the re- distributions which forces produce in organic matter; and here we must take a like survey of the simultaneous re-distributions undergone by the forces.
At the outset we are met by a difficulty. The parts of an inorganic mass undergoing re arrangement by an incident force, are, in most cases, passive — do not complicate those necessary re- actions that result from their inertia, by other forces which they originate. But in organic matter, the re-arranged parts do not re-act in virtue of their inertia only: they are so constituted that the incident force usually sets up TllK RE-ACTIONS OF OlKiANIC MATTER ON FORCES. 4*5 in them, other actions wliich are much more important. Indeed, what we may call the indirect re-actions thus caused, are so great in their amounts compared with the direct re- actions, that they quite obscure them.
In strictness, these two kinds of re-action should not bo dealt with together. The impossibility of separating them, however, compels us to disregard the distinction between them. Under the above general title, we must include both the immediate re-actions and those re-actions mediately produced, which are among the most conspicuous of vital phenomena.
§ 18. From organic matter, as from all other matter, incident forces call forth that re-action which we know as heat. More or less of molecular vibration almost necessarily results, when, to the forces at work among the molecules of any aggregate, other forces are added. Experiment abundantly demonstrates this in the case of inorganic masses; and it must equally hold in the case of organic masses. In both cases the force which, more markedly than any other, produces this thermal re-action, is that which causes the union of different substances with each other. Though inanimate bodies admit of being greatly heated by pressure and by the electric current, yet the evolutions of heat thus induced, are neither so common, nor in most cases so conspicuous, as those resulting from chemical combination. And though in animate bodies, there are doubtless certain amounts of heat generated by other actions; yet these are all secondary to the heat generated by the action of oxygen on the substances composing the tissues and the substances contained in them. Here, however, we see one of the characteristic distinctions between inani- mate and animate bodies. Among the first, there are but few which ordinarily exist in a condition to evolve the heat caused by chemical combination; and such as are in this condition soon cease to be so, when chemical combination 44 THE DATA OF BIOLOGY.
and genesis of heat once begin in them. Whereas among the second, there universally exists the ability, more or less decided, thus to evolve heat; and the evolution of heat, in some cases very slight and in no cases very great, continues as long as they remain animate bodies.
The relation between active change of matter and re-active genesis of atomic vibration, is clearly shown by the contrasts between different organisms, and between different states and parts of the same organism. In plants, the genesis of heat is extremely small, in correspondence with their extremely small production of carbonic acid: those portions only, as flowers and germinating seeds, in which considerable oxidation is going on, having a decidedly raised temperature. Among animals, we see that the hot-blooded are those which expend much force and respire actively. We see that though such creatures as insects are scarcely at all warmer than the surround- ing air when they are still, they rise several degrees above it when they exert themselves; and that in creatures like our- selves, which habitually maintain a heat much greater than that of their medium, exercise is accompanied by an ad- ditional production of heat, often to an inconvenient extent.
This molecular agitation accompanying the molecular re- arrangements that are caused by oxygen taken into the animal organism, must result both from the union of oxygen v^ith those nitrogenous matters of which the tissues are composed, and from its union with those non-nitrogenous m.atters which are diffused through the tissues. Just as much heat as would be caused by the oxidation of such matters out of the body, must be caused by their oxidation in the body. In the one case as in the other, the heat must be re- garded as a concomitant. Whether the distinction, made by Liebig between nitrogenous substances as tissue- food, and non-nitrogenous substances as heat-food, be true or not in a narrower sense, it cannot be accepted in the sense that tissue-food is not also heat-food. Indeed he does not himself assert it in this sense. The ability of carnivorous THE RE-ACTIONS OF ORGANIC MAITER ON FORCES. 45 animals to live and generate heat while consuming matter that is almost exclusively nitrogenous, to say nothing of the con- stant relation above shown between functional activity and the evolution of heat, suffices to prove that the nitrogenous com- pounds forming the tissues are heat- producers, as well as the non-nitrogenous compounds circulating among and through the tissues. But it is possible that this antithesis is not true even in the more restricted sense. It seems quite an admissible hypothesis that the hydro-carbons and oxy-hydro- carbons which, in traversing the system, are transformed by communicated chemical action, evolve during their transform- ation, not heat alone, but also other kinds of force. It may be that as the nitrogenous matter, while falling into more stable molecular arrangements, generates both that molecular agi- tation called heat, and such other molecular movements as are resolved into forces expended by the organism; so, too, does the non-nitrogenous matter. Or perhaps the concomitants of this metamorphosis of non- nitrogenous matter, vary with the conditions. Heat alone may result when it is transformed while in the circulating fluids, but partly heat, and partly another force, when it is transformed in some active tissue that has absorbed it: just as coal, though producing little else but heat as ordinarily burnt, has its heat partially transformed into mechanical motion if burnt in a steam-engine furnace. In such case, the antithesis of Liebig would be reduced to this; — that whereas nitrogenous substance is tissue-food both as material for building-up tissue and as material for its function; non-nitrogenous substance is tissue- food only as material for function.
There can be no doubt that this thermal re-action which chemical action from moment to moment produces in the body, is from moment to moment an aid to further chemical action. We before saw {First Princijoles, § 103) that a state of raised molecular vibration, is favourable to those re-dis- tributions of matter and motion which constitute Evolution. \ye saw that in organisms distinguished by the amount and 46 THE DATA OF BIOLOGY.
rapidity of such re-distributions, this raised state of molecular vibration is conspicuous. And we here see that this raised state of molecular vibration, is itself a continuous consequence of the continuous molecular re- distributions it facilitates. The heat generated by each increment of chemical change, makes possible the succeeding increment of chemical change. In the body this connexion of phenomena is the same as we see it to be out of the body. Just as in a burning piece of wood, the heat given out by the portion actually combining with oxygen, raises the adjacent portion to a temperature at which it also can combine with oxygen; so, in a living animal, the heat produced by oxidation of each portion of tissue, maintains the temperature at which the unoxidized portions can be readily oxidized.
§ 19. Among the forces called forth from organisms by re-action against the actions to which they are subject, is Light. Phosphorescence is in some few cases displayed by plants — especially by certain fungi. Among animals it is comparatively common. All know that there are several kinds of luminous insects; and many are familiar with the fact that luminosity is a characteristic of various marine creatures.
Most of the evidence goes to show that this evolution of light, as well as the evolution of heat, is consequent on oxi- dation of the tissues. Light, like heat, is the expression of a raised state of molecular vibration: the difference between them being a difference in the rates of vibration. Hence by chemical action on substances contained in the organism, heat or light may be produced, according to the character of the resulting molecular vibrations. The inference that oxidation is the cause of this luminosity, does not, however, rest only on a priori grounds. It is supported by experi- mental evidence. In phosphorescent insects, the continuance of the light is found to depend on the continuance of respira- tion; and any exertion which renders respiration more active, THE RE- ACTIONS OF ORGANIC MATTER ON FORCES. 47 increases the brilliancy of the light. Moreover, by separating the luminous matter, Prof. Matteucci has shown that its emission of light is accompanied by absorption of oxygen and escape of carbonic acid. The phosphorescence of marine animals has been referred to other causes than oxidation. In some cases, however, it is, I think, explicable without assuming any more special agency. Considering that in creatures of the genus Noctiluca^ for example, ^to which the phosphorescence most commonly seen on our own coasts is due, there is no means of keeping up a constant circulation, we may infer that the movements of aerated fluids through their tissues, must be greatly affected by impulses received from without. Hence it may be that the sparkles visible at night when the waves break gently on the beach, or when an oar is dipped into the water, are called forth from these creatures by the concussion, not because of any unknown influence it excites, but because, being propagated through their delicate tissues, it produces a sudden movement of the fluids and a sudden increase of chemical action. Neverthe- less, in other phosphorescent animals inhabiting the sea, as in the Pyrosoma and in certain Annelida, light seems to be really produced, not by direct re-action on the action of oxygen, but by some indirect re-action involving a trans- formation of force.
§ 20. The re-distributions of matter in general, are accom- panied by electrical disturbances; and there is abundant evidence that electricity is generated during those re- distri- butions that are ever taking place in organisms. Experi- ments have shown " that the skin and most of the internal membranes are in opposite electrical states; " and also that between different'internal organs, as the liver and the stomach, there are electrical contrasts — such contrasts being greatest where the processes going on in the compared parts are most unlike. It has been proved by M. du Bois-Eeymond that when any point in the longitudinal section of a muscle is 48 THE DATA OF BIOLOGY.
connected by a conductor with any point in its transverse section, an electric current is established; and further, that like results occur when nerves are substituted for muscles. The special causes of these phenomena have not yet been determined. Considering that the electric contrasts are most marked where active secretions are going on — considering, too, that while they do not exist between external parts which are similarly related to the vascular currents, they do exist between external parts which are dissimilarly related to the vascular currents — and considering also that they are extremely difficult to detect where there are no appre- ciable movements of fluids; it may be that they are due simply to the friction of heterogeneous substances, which is universally a cause of electric disturbance. But whatever be the interpretation, the fact remains the same, that there is throughout the living organism, an unceasing production of differences between the electric states of different parts; and consequently an unceasing restoration of electric equilibrium by the establishment of currents among these parts.
Besides these general, and not conspicuous, electrical phe- nomena which appear to be common to all organisms, vegetal as well as animal, there are certain special and strongly marked ones. I refer, of course, to those which have made the Torpedo and the Gymnotiis objects of so much interest. In these creatures we have a genesis of electricity that is not incidental on the performance of their different functions by the different organs; but one which is itself a function, having an organ appropriate to it. The character of this organ in both these fishes, and its largely-developed con- nexions with the nervous centres, have raised the suspicion, which various experiments have thus far justified, that in it there takes place a transformation of what we call nerve- force into the force known as electricity: this conclusion being more especially supported by the fact, that substances, such as morphia and strychnia, which are known to be powerfu THE RE-ACTIONS OF ORGANIC MATTER ON FORCES. 49 nervous stimulants, greatly increase the violence and rapidity of the electric discharges.
But whether general or special, and in whatever manner produced, these evolutions of electricity are among the re-actions of organic matter, called forth by the actions to which it is subject. Thougli these re-actions are not direct, but seem rather to be remote consequences of those changes wrought by external agencies on the organism, they are yet incidents in that general re-distribution of motion, which these external a2:encies initiate; and as such must here be noticed.
§ 21. To these known modes of motion, has next to bo added an unknown one. Ileat, Light, and Electricity are emitted by inorganic matter when undergoing changes, as well as by organic matter. But there is a kind of force mani- fested in some classes of living bodies, which we cannot identify with any of the forces manifested by bodies that are not alive, — a force which is thus unknown, in the sense that it cannot be assimilated with any otherwise-recognized class. I allude to what is called nerve- force.
This is habitually generated in all animals, save the lowest, by incident forces of every kind. The gentle and violent mechanical contacts, which in ourselves produce sensations of touch and pressure — the additions and abstractions of mole- cular vibration, which in ourselves produce sensations of heat and cold; produce in all creatures that have nervous systems, certain nervous disturbances — disturbances which, as in ourselves, are either communicated to the chief nervous centre, and there constitute consciousness, or else result in merely physical processes that are set going elsewhere in the organism. In special parts distinguished as organs of sense, other external actions bring about other nervous re-actions; that show themselves either as special sensations, or as ex- citements which, without the intermediation of consciousness, i 50 THE DATA OF BIOLOGY.
beget actions in muscles or other organs. Besides neural discharges that follow the direct incidence of external forces, there are others ever being caused by the incidence of forces which, though originally external, have become internal by absorption into the organism of the agents exerting them. Por thus may be classed those neural discharges that from moment to moment result from modifications of the tissues, wrought by substances carried to them in the blood. That the unceasing change of matter which oxygen and other agents produce throughout the system, is accompanied by a genesis of nerve-force, is shown by various facts; — by the fact that nerve-force is no longer generated, if oxygen be with- held, or the blood prevented from circulating; by the fact that when the chemical transformation is diminished, as during sleep \Yith. its slow respiration and circulation, there is a diminution in the quantity of nerve-force; in the fact that an excessive expenditure of nerve-force, involves excessive re- spiration and circulation, and excessive waste of tissue. To these proofs that nerve-force is evolved in greater or less quan- tity, according as the conditions to rapid molecular change throughout the body, are well or ill fulfilled; may be added proofs that certain special molecular actions, are the causes of these special re-actions. The eflects of alcohol, ether, chloroform, and the vege to -alkalies, put beyond doubt the inference, that the overthrow of molecular equilibrium by chemical afiinity, when it occurs at certain places in the body, results in the overthrow of equilibrium in the nerves pro- ceeding from these places — results, that is, in the propagation through these nerves, of the change called a nervous dis- charge. Indeed, looked at from this point of view, the two classes of nervous changes — the one initiated from without and the other from within — are seen to merge into one class. Both of them may be traced to metamorphosis of tissue. There can be little doubt that the sensations of touch and pressure, are consequent on accelerated changes of matter, produced by mechanical disturbance of the mingled TJIK UK- ACTIONS OF ORGANIC MATTER ON FORCES. 51 fluids and solids composing the parts affected. There is abundant evidence that the sensation of taste, is due to the chemical actions set up by particles which find their way through the membrane covering the nerves of taste; for, as Prof. Graham points out, sapid substances all belong to the class of crystalloids, which are able rapidly to permeate animal tissue, while colloids, which cannot pass through animal tissue, are all insipid. Similarly with the sense of smell. Substances which excite this sense, are necessarily more or less volatile: and their volatility being the result of their molecular mobility, implies that they have in a high degree, the power of getting at the olfactory nerves by pene- trating their mucous investment. Again, the facts which photography has familiarized us with, make it clear that those nervous impressions called colours, are primarily due to certain changes wrought by light in the substance of the retina. And though, in the case of hearing, we cannot so clearly trace the connexion of cause and effect; yet as we see that the auditory apparatus is one fitted to intensify those vibrations constituting sound, and to convey them to a recep- tacle containing fluid in which nerves are immersed; it can scarcely be doubted that the sensation of sound proximately results from atomic re-arrangements caused in these nerves by the vibrations of the fluid: knowing, as we do, that the re-arrangement of atoms is in all cases aided by agita- tion. Perhaps, however, the best proof that nerve- force, whether peripheral or central in its origin, results from chemical transformation, lies in the fact that most of the chemical agents which powerfully affect the nervous system, affect it whether applied at the centre or the periphery. Vari- ous acids, mineral and vegetal, are tonics — the stronger ones being usually the stronger tonics; and this which we call their acidity, implies a power in them of acting on the nerves of taste, while the tingling or pain that follows their absorp- tion through the skin, implies that the nerves of touch are acted on by them. Similarly with certain vegeto-alkalics i* 52 THE DATA OF BIOLOGY.
which are peculiarly bitter. These by their bitterness, show that they affect the extremities of the nerves; while by their tonic properties, they show that they affect the nervous centres — the most intensely bitter among them, strychnia, being the most powerful nervous stimulant. However true it may be that this relation is not a regular one, since opium, hashish, and some other drugs, which work marked effects on the brain, are not remarkably sapid — however true it may be that there are relations between particular substances and particular parts of the nervous system; yet such instances do but qualify, without negativing, the general proposition. The truth of this proposition can scarcely be doubted when, to the evidence above given, is added the fact that various condiments and aromatic drugs are given as nervous stimu- lants; and the fact that anaesthetics, besides the general effects they produce when inhaled or swallowed, produce local effects of like kind when absorbed through the skin; and the fact that ammonia, which in consequence of its extreme molecular mobility, so quickly and so violently excites the nerves be- neath the skin, as well as those of the tongue and the nose, is a rapidly-acting stimulant when taken internally.
Whether we shall ever know anything more of this nerve- force, than that it is some species of molecular disturbance that is propagated from end to end of a nerve, it is impossi- ble to say. Whether a nerve is merely a conductor, which delivers at one of its extremities an impulse received at the other; or whether, as some now think, it is itself a generator of force which is initiated at one extremity and accumulates in its course to the other extremity; are also questions which cannot yet be answered. All we know is, that forces capable of working molecular changes in nerves, are capable of callino- forth from them manifestations of activity — dis- charges of some force, which, though probably allied to elec- tricity, is not identical with it. And our evidence that nerve- force is thus originated, consists not only of such facts as the above, but also of more conclusive facts established by direct TIIF. RE-ACTIONS OF ORGANIC MAITER ON FORCES. 53 experiments on nerves — experiments wliicli sliow that nerve- force is irenerated when the cut end of a nerve is cither me- chanically irritated, or acted on by some chemical agent, or subject to the galvanic current — experiments which thus prove that nerve-force is liberated by whatever disturbs the molecular equilibrium of nerve-substance. And this is all which it is necessary for us here to understand, § 22. The most important of these re-actions called forth from organisms by surrounding actions, remains to be noticed. To the above various forms of insensible motion thus caused, we have to add sensible motion. On the production of this mode of force, more especially depends the possibility of all vital phenomena. It is, indeed, usual to regard the power of generating sensible motion, as confined to one out of the two organic sub-kingdoms; or, at any rate, as possessed by but few members of the other. On looking closer into the matter, however, we see that plant-life as well as animal-life, is uni- versally accompanied by certain manifestations of this power; and that plant-life could not otherwise continue.