« AnteriorContinuar »
The discussion of this subject has, as you no doubt are well aware, recently chiefly become centred in the question of the irritability of muscle, a question which has proved so difficult for the very reason that the possession of irritability was restricted by Haller with great exclusiveness to muscle. Haller with the greatest obstinacy combated the opinion that any other part was irritable; and curiously enough he even contested the irritability of parts, which, as the minuter investigations of later observers have shewn, contain muscular elements, as for example, the middle coat of the vessels. Indeed, he made use of tolerably energetic expressions when repudiating the excitability of the vessels, which even then was maintained by others. I have already informed you that there are large tracts in the vascular system (for example, in the umbilical vessels of the fetus, where they are particularly well marked) in which enormous accumulations of muscular fibres are found, but not a trace of any nerves. Here irritability exists in a high degree; we can produce contractions of the muscles mechanically, chemically and electrically. Just the same is the case with many other, small vessels, which by no means exhibit nervefibres in all their parts. In them too we can at every single point where muscles exist, at once provoke contraction.
The solution of this question has recently, as is well known, been particularly promoted by the fact that, by the employment of certain poisons, especially the woorara poison, observers have succeeded in paralyzing the nerves right down to their extreme terminations, or at least as far as these were accessible to the experiment; and this in such a manner, that the objection cannot well be raised, that the excitability of the extreme terminations of the nerves contained in the muscle is preserved. The paralysis produced by the woorara poison is completely confined to the nerves, whilst the muscles just as completely retain their irritability. Whilst the most violent electrical currents were made to act upon the nerve in vain, without the production of the least
NUTRITIVE IRRITABILITY. 295
movement, the slightest mechanical, chemical or electrical stimuli are sufficient to throw the muscle experimented upon into a state of excitation.
I have mentioned these facts to you, in order that I might not be thought to treat the different divisions of my subject too unequally. The question of function, however, interests us less here. Nevertheless, you will be able to gather from what I have communicated to you, that now-a-days it can no longer be said with any shew of reason that the nerves alone are irritable parts, but that we are irresistibly led to consider functional irritability, at least, as fl property belonging to whole series of organs.
Far less known, gentlemen, is that clearly demonstrable series of processes in which nutritive irritability manifests itself—that power possessed by individual parts of taking up, when excited by definite stimuli, more or less matter and transforming it. This constitutes at the same time the first step in the most important processes which we have to follow into the domain of pathologico-anatomical facts.
A part, which nourishes itself, can in doing so either limit itself to a mere maintenance of its existence, or it may, as is especially seen in pathological cases, take up into itself a larger quantity of nutritive material than is wont to happen in the ordinary course of things. If we investigate these processes of absorption more closely, we always find that, as I have already had occasion to remark to you, the number of histological elements remains the same before and after the occurrence of the excitation; and we thus distinguish simple hypertrophies from the hyperplastic conditions, to which, in their external effects, they often bear so great a resemblance (p. 65, Pig. 27, B). It is, however, of extreme importance for the attainment of correct pathological notions, that we should know that a part, which in virtue of some inherent power, takes up a large quantity of material, need not on that account necessarily fall into B permanent condition of enlargement, but that, on the contrary, under these very circumstances there often arises subsequently in its internal economy a disturbance which imperils the persistence of the part and becomes the proximate cause of its destruction. There are, as we know from experience, certain limits to the enlargement of every tissue, within which it is able to maintain a regular existence; if these limits be exceeded, and especially, if suddenly, we always see that obstacles spring up impeding the further life of the part, and that when the process runs a particularly acute course, a weakening of the part sets in, proceeding to a complete destruction of it. Processes of this kind form a part of that domain which in ordinary life is assigned to inflammation. A number of inflammatory processes on their first appearance really exhibit nothing more than an increased assumption of material into the interior of the cells, entirely resembling what we find in simple hypertrophy. If, for example, we consider the history of Bright's disease in its ordinary course, we constantly find, that the very first thing which can be detected in a kidney affected with this disease, consists in this, that in the interior of the uriniferous tubules whilst still quite intact, the individual epithelial cells which are, as is well known, even in their normal state tolerably large, become still larger. These epithelial cells which fill up the tubules are not only large,
Fig 93 but a* *ne same ^me a^° present a
very cloudy appearance, inasmuch as a larger quantity of material than usual has everywhere been taken up into the cells. The entire uriniferous tubule is thereby rendered broader, and appears even to the naked eye as a convoluted, whitish, opaque body. If we isolate the individual cells, which is somewhat
Fig. 9S. Convoluted urinary tubule from the cortex of the kidney iu morbus Brightii. a. Tolerably normal epithelium, b, state of cloudy swelling, c, comCLOUDY SWELLING. 297
difficult, as the cohesion of the particles composing them has usually begun to suffer, we find in them a granular mass apparently containing nothing else than the granules which are normally present in the interior of the cells, but which accumulate in greater numbers the greater the energy with which the process is carried on, so that even the nucleus gradually grows indistinct. This is the condition of cloudy swelling (triibe Schwellung), as it is met with in many irritated parts, as an expression of the irritation which attends many forms of what is called inflammation. From these processes backwards to the phenomena of simple hypertrophy we find no recognizable boundaries at all. We cannot at once say, when we meet with a part enlarged in this way, and containing a greater amount of matter than usual, whether it will retain its life or perish; and therefore it is extremely difficult in very many cases, when nothing at all is known concerning the process through which such a change has been produced, to distinguish simple hypertrophy from those forms of inflammatory processes which are essentially accompanied by an increased absorption of nutritive material.
In these processes too it is scarcely possible to refuse the individual elements, when incited by a stimulus directly applied to them, the power of taking up an increased quantity of material; at least it is opposed to all the results of experience, to assume that such an increased absorption must be due to a special innervation. If we select a part which, in accordance with all observation, is entirely destitute of nerves, as for example, the surface of an articular cartilage, we can, as was shewn many years ago by the beautiful experiments of Redfern, produce altogether similar effects by means of direct stimuli. In precisely the same way, there are not unfrequently observed, in chronic diseases of cartilage, nodular elevations of the surface; and upon examining such spots microscopically we find the same thing that I shewed you in a former lecture in a costal cartilage (p. 21, Fig. 9), namely, that the cells which at other times are very delicate, small, lenticular bodies, increase in size, swell up into large, round corpuscles, and in proportion as they take up more matter, enlarge in all directions, so that at last the whole spot forms a little protuberance above the surface. Now in articular cartilage no nerves at all are found; the terminal ramifications of those nearest to it are at best situated in the medulla of the bone immediately adjoining, and that, perhaps, is separated from the irritated spot of the surface by an intact, intervening layer of cartilaginous tissue one or two lines in thickness. Now it would indeed be contrary to all experience, to conceive that a nerve could from the medulla of the bone exercise a special action upon the cells of the surface of the cartilage, which were the seat of irritation, without a simultaneous affection of the cells lying between the nerve and the irritated spot. If we draw a thread through a cartilage, so that merely a traumatic irritation is produced, we see that all the cells which lie close to the thread become enlarged through an increased absorption of material. The irritation produced by the thread extends only to a certain distance into the cartilage, whilst the more remote cells remain altogether unaffected. Such observations cannot be explained otherwise than by assuming that the stimulus really acts upon the parts to which it is applied; it is impossible to conclude that it is conducted to the nerve by any channel perhaps more in accordance with the neuro-pathological doctrine, and then only by reflex action conveyed back again to the parts.
mciicing fatty metamorphosis and disintegration. At b and c increased breadth of the tubule. 300 diameters.