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DIRECT IRRITATION OF TISSUES. 299

dantly supplied with nerves, we find in every case, that the extent of the irritation, or to speak more accurately, the extent of the irritated area, by no means corresponds to the size of any particular nerve-territory, but that in a tissue in other respects normal the size of the affected area essentially corresponds to that of the local irritation. If we make the experiment with the thread, upon the skin, a whole series of nerve-territories are intersected by it. Still the whole of the territories belonging to the nerves which lie along the thread, are not thrown into the same morbid condition, but the nutritive irritation is limited to the immediate vicinity of the thread. No surgeon expects in operations of the kind, that all the nerve-territories traversed by the thread, will become diseased in their whole extent. Great complaints would have to be raised against nature, if every ligature, every seton were to exercise an irritating influence, beyond the limits of the parts with which it is in immediate contact, upon the whole extent of the nerve-districts which it passes through. Thus we see in a tissue in which what takes place in such a case can be very clearly traced, namely in the cornea, that in parts of it to which no vessels extend, there are certainly still nerves which possess a reticular arrangement, and leave larger and smaller districts of tissue between them altogether devoid of nerves. Now if we apply any stimulus directly to the cornea, as for example, a red hot needle, or lunar caustic, the district which is thereby set in morbid action by no means corresponds to the distribution of any nerve. It once happened to me with a rabbit that the cautery lighted precisely upon a nervous filament, but the morbid action remained confined to the immediate vicinity of this spot, and by no means spread over the whole district appertaining to the nerve.

It is therefore utterly impossible, even if observations, like those on cartilage which I have laid before you, are not allowed to have any weight, not to admit that the phenomena of irritation in parts supplied with nerves are in no respect different from those which occur in nerveless parts, and that the immediate effects essentially depend upon the enlargement and tumefaction of the surrounding elements, so that when there are many of them, a visible swelling of the whole part is the result. This is what you observe when a ligature is anywhere drawn through the skin. If on the following day the immediate vicinity of the thread be examined, an active enlargement of the cellular elements is found, quite irrespective of the distribution of vessels and nerves in the part.

There is, as you see, an essential difference between what I here lay down and the opinions which have generally been advanced with regard to the proximate causes of these swellings. According to the old maxim: ubi stimulus, ibi affluxus, it was generally conceived that the first thing which took place was an increased afflux of blood (which was itself referred by the neuro-pathologists to the excitation of sensitive nerves), and then that the immediate consequence of the increased afflux was an increased excretion of fluid from the blood, constituting the exudation which filled the part.

In the first timid attempts which I made to alter this conception, I employed the expression parenchymatous exu

1 The term Parenchyma was first employed by Erasistratus of Alexandria to designate the mass of tissue which lies between the vessels of a part, and in his opinion formed a kind of affusion from them. Thus Galen says (Isagoge s. Introductio, cap. xi): "Cerebrum ex nullo principal! vase compositum esse videtur Erasistrato, eoque nutrimenti parenchyma, i. e., affusio, ipsi esse videtur." In the same way the word is used by Vesalius (De humani corp. fabrics, lib. V, cap. 7) and by Thorn. Bartholin (Anatome, lib. I, cap. 14), for the proper substance of the liver, lying external to, or between, the vessels. It therefore essentially denotes the tissue of which an organ is constituted. In a narrower sense those constituents of an organ which are peculiar to it, and give it its specific character, may be distinguished as its proper parenchyma, in contradistinction to its merely interstitial tissue. In my book the term has been used in both of these senses.—From a US. note by the Author.

PARENCHYMATOUS KERATITIS. 301

dation, retaining the term exudation, out of deference to prevailing opinion. I had, namely, convinced myself that in many places where a swelling had occurred, there was absolutely nothing else to be seen than tissue. In a tissue which consisted of cells, I could, after the swelling (exudation) had taken place, still see nothing but cells; in tissues composed of cells and intercellular substance, nothing but cells and intercellular substance; the individual elements indeed were larger, fuller, and filled with a quantity of matter with which they ought not to have been filled, but there was no exudation in the manner in which it had been imagined to exist, namely free, or in the interstices of the tissue. All the matter was contained in the elements of the tissues themselves. This was what I intended to express by the term, parenchymatous exudation, and hence the name, parenchymatous inflammation, is derived—a name which was, indeed, used in former times, but in quite another sense from that I meant—and which is now more generally employed than is perhaps desirable. It is, however, at all events important that you should draw a distinct line of demarcation between this form of irritation as a general standard and the other forms (especially the formative one), inasmuch as in it only the constituent elements of a tissue already existing in the body take up a larger quantity of material, and besides these enlarged elements nothing else is present.

I will immediately send round a preparation to you, in which you will see a very characteristic example of such an inflammation. It is almost the most striking example which for a long time has come before me. It is a specimen from a case of so-called Keratitis, from one of Herr von Graefe's patients, in whom, after violent, diffuse phlegmonous inflammation of the extremities, an extremely rapid inflammatory opacity of the cornea took place. When the cornea was put into my hands, it seemed to me as if it were opaque and swollen in its whole thickness. The vessels a section through the part, it at once became evident, even with a low power, that the opacity extended by no means uniformly throughout the whole cornea, but was limited to a definite portion of the tissue. This portion is so characteristic in reference to the different explanations possible, that the case, I think, presents especial interest, theoretically.

of the borders were very full of blood. But when I made

Fig. 99.

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It turned out namely that the opacity began in the immediate proximity of the posterior surface and at the circumference of the cornea, close to the membrane of Descemet (posterior elastic lamina of Bowman) at the point where the iris is attached. Thence the opacity, assuming almost the shape of a flight of steps, mounted up into the cornea till within fl certain distance of the external surface. Then it proceeded at the same level, till it descended upon the other side again in a similar manner. Thus an opaque bow was formed throughout the whole substance of the cornea, without reaching the external (anterior) surface and without encroaching upon the central parts of the posterior

Fig. 99. Parenchymatous keratitis. A, A. Anterior (external), B, B, posterior (internal) side of the cornea. C, C. The clouded zone with enlarged cornea-corpuscles. 18 diameters.

STRUCTURE OF THE CORNEA.

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surface. If we imagine the nutrition of the cornea to proceed from the aqueous humour, the opacity did not assume the form that might have been looked for, for then we should rather have expected that the hindermost layer would be the first to undergo the change. If any influence from without had been here in operation, the opacity must have been seated in the most anterior layers; if again the opacity were one which essentially proceeded from the vessels, we might, inasmuch as they chiefly lie along the border and nearer to the anterior surface, have expected to find the principal disease there. Finally, if the changes had their origin in the nerves, we should have found the opacity spread in the form of a network on the surface—and not a bow of this kind.

The substance of the cornea consists, you know, according to general opinion, of lamellae (plates) which run in a more or less parallel direction through the cornea. Now

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Fig. 100. Perpendicular section of the cornea of the ox, for the purpose of shewing the form and anastomoses of its cells (corpuscles). Here and there are seen the cut ends of some of the processes of the cells, looking like fibres or points. 500 diameters. From His, 'Wiirzb. Verhandl.,' IV, plate IV, fig. I.

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