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tions that are instituted concerning life and vital activity— that, namely, in all parts of the body a splitting up into a number of small centres takes place, and that nowhere, as far as our experience extends, does a single central point susceptible of anatomical demonstration exist, from which the operations of the body are carried on in a perceptible manner. And even if we appeal to the experience which every one daily stores up around him, we shall find that this is the only view which concedes life to the individual parts of an organism, or allows it to the plant—the only view which enables us to institute a comparison both between the collective life of the developed animal and the individual life of its smallest parts; and also between the life of a plant as a whole and the life of the individual parts of a plant.

The opposite view which at this very moment is manifesting itself with a certain degree of energy—that namely, which beholds in the nervous system the real central point of life—is met by this extremely great difficulty, that, in the very same apparatus, in which it places its unity, it again finds the same splitting up into an infinite number of separate centres, which is presented by the rest of the body ; and that in no part of the whole nervous system it can shew the real central point, from which, as from a seat of government, mandates are issued to all quarters.

It may seem very convenient to say that the nervous system constitutes the real unity of the body, inasmuch as there is certainly no other system, which enjoys such a complete dissemination throughout the most various peripheral and internal organs. But even this wide dissemination and the numerous connections which exist between the individual parts of the nervous system, are by no means calculated to shew it to be the centre of all organic actions. We have found in the nervous system definite little cellular elements which serve as centres of motion, but we do


not find any single ganglion-cell in which alone all movement in the end originates. The most various individual motory apparatuses are connected with the most various individual motory ganglion-cells. Sensations are certainly collected in definite ganglion-cells, still among them too we do not find any single cell which can in any way be designated the centre of all sensation, but we again meet with a great number of very minute centres.

All the operations which have their source in the nervous system, and there certainly are a very great number of them, do not allow us to recognise a unity anywhere else than in our own consciousness; an anatomical or physiological unity has at least as yet been nowhere demonstrable. If we really were to set down the nervous system with its numerous separate centres as the central point of all organic actions, even then the thing actually sought for, a real unity, would not have been obtained. If a clear idea is formed of the difficulties which stand in the way of such a unity, it can scarcely be doubted, but that we are continually led astray by the spiritual phenomena displayed in our own persons, in the interpretation of organic processes. Feeling ourselves to be something simple and indivisible, we always start with the presumption that everything else must be regulated by this indivisible principle. But if we trace the development of any given plant from its first germ up to the highest point in its evolution, we meet with a series of processes altogether analogous, without our being able to entertain the supposition for a moment, that such a unity exists in it, as we are led by our consciousness to suppose exists in us. Nobody has been able to detect a nervous system in plants; in no case has it been discovered that the whole of the fully developed plant was governed from a single point. All the vegetable physiology of the present day is based upon the investigation of the activity of cells, and if violent opposition is still made to the introduction of the same principle also into the animal economy, there is, I think, no other difficulty in the way but the one, that aesthetical and moral scruples cannot be overcome.

It cannot of course here be our business either to refute these scruples or to point out how they might be reconciled with the views I advocate. I have only to shew in how great a degree the pathological processes which especially interest us, in all cases conduct us back to the same cellular principle, and how much they are in every case opposed to that notion of a single controlling principle, which is sought to be established by the neuropathologists. This opinion of mine has after all really nothing new or uncommon in it. If for thousands of years the life of the individual parts of the body has been talked about, if the position is admitted, that in diseased conditions the death of individual parts, necrosis or gangrene in them may take place, whilst the whole still continues to exist—the inference is, that something of our way of thinking had long been expressed in the views held by the world in general: only people had not formed very clear notions upon the subject. If we speak of the life of the individual parts of a body, we must also know in what way life manifests itself, and whereby it is essentially characterized. This characteristic we find in activity, an activity indeed, in which there is displayed by every single part, whilst it contributes its contingent, according to its peculiarities, to the general activity of the body—something identical with the life of the other parts; for else we should be in no way justified in regarding life as something in every case similar, and derivable from some common origin.

This vital activity is, as far at least as we are able to judge, nowhere, in no part whatever, carried on by means of any cause allotted to it from the very beginning, and IRRITABILITY. 287

entirely confined to it, but we everywhere see that a certain excitation is necessary for its production. Every vital action presupposes an excitation, or if you like an irritation. The irritability of a part, therefore, appears to us the criterion, by which we can judge whether it is alive or not. Whether, for example, a nerve be alive or dead, we cannot immediately determine by an anatomical examination of it, conducted either microscopically or macro scopically. In the outward appearance, in the more obvious structural arrangements, which we are able to decipher by the aid of our auxiliaries, we rarely find sufficient to enable us to come to a decision upon a point such as this. Whether a muscle is alive or dead, we are but little able to judge, inasmuch as we find its structure still preserved in parts which perished years ago. I found in a fetus, which in a case of extra-uterine pregnancy, had lain thirty years in the body of its mother, the structure of the muscles as intact, as if it had just been born at its full time. Czermak examined parts of mummies, and found in them a number of tissues which were in a state of such perfect preservation, that the conclusion might very well have been come to, that the parts had been taken from a living body. Our notion of the death, decease, or necrosis of a part, is based upon nothing more or less than this, that whilst its form is preserved, and indeed in spite of it, we can no longer detect any irritability in it. This has been most clearly shewn quite recently in the course of some investigations into the more hidden properties of nerves. Now that, by the investigations of Dubois, activity has been shewn to exist in nerves even when in a so-called state of repose, and that it has been discovered, that in a nerve, even when seemingly at rest, electrical processes are continually going on, and that it constantly produces an effect upon the magnetic needle—now we are able, by means of this physical experiment, with certainty to judge when a nerve is dead, for, as soon as death has stepped in, those qualities cease, which are inseparably connected with the life of the nerve.

This peculiarity which we find in some parts exhibited in such a marked degree and so evidently demonstrable, becomes less and less apparent, the more lowly the organization of the part, and our criteria are least to be depended upon in the case of the class of connective tissues; for we are, indeed, really frequently much puzzled to decide whether a part composed of one of them is still alive or has already perished.

If now we proceed with our analysis of what is to be included in the notion of excitability, we at once discover, that the different actions which can be provoked by the influence of any external agency, are essentially of three kinds; and I consider it of great importance that you should pay particular attention to this point, as it will greatly assist you in the classification of pathological conditions, and because it is not wont to be set forth with particular distinctness.

When, namely, a given action is called into play, we have to deal with a manifestation either of the function, the nutrition, or Conformation of a part. It certainly cannot be denied that at certain points the boundaries between these different processes disappear, and that between the nutritive and formative processes, and also between the functional and nutritive ones, there are transitional stages; still, when they are typically performed, there is a very marked difference between them; and the internal changes which the individual excited part undergoes, according as it only performs its functions, or is subjected to a special nutrition, or becomes the seat of special formative processes, exhibit considerable differences. The result of an excitation, or if you will, an irritation, may, according to circumstances, be either a merely functional process; or the effect may be that a more or less increased

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