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and accordingly it was with these my first experiments were made. I need scarcely add, that when solution^ of these two salts come in contact with each other, a beautiful blue precipitate takes place, which is in fact the well-known pigment called prussian blue. Besides these, I have used for transparent parts solutions of the muriate of barytes, and an alkaline sulphate; also a concentrated filtered solution of the coloring matter of cochineal and the muriate of tin; the former producing a white precipitate, the latter a red one, or, in fact, carmine.

With respect to the strength of these solutions, I have generally used the prussiate of potass, the muriate of barytes, and the infusion of cochineal, in nearly a saturated state, especially the last; the two former, when in a state of saturation, may be diluted with about an equal quantity of distilled water. The other solutions must be much weaker, especially the sulphate of iron, a few drops of a saturated solution of which to the ounce of distilled water will be found sufficient. The best way is, however, to ascertain previously by experiment the strength of the three last injected fluids, which must be such as just to produce a full precipitate, and no more.

I do not mean to say that these are the only solutions that can be made use of for this mode of injection; no doubt ethers, and perhaps preferable ones, might be pointed out; but I confine myself to these, as they are the only ones I have submitted to experiment. As to the steps preliminary to injection, they are nearly such as commonly observed; I would, however, recommend the pipe to be fixed, when the artery is small, before the part be soaked, as it has been found no easy matter to do it afterwards. It is then to be put into water of the temperature of from 90 to 100, and suffered to remain till thoroughly heated, when the solutions previously heated to the same temperature, and contained in different syringes adapted to the same pipe, are to be injected one after the other. As both the fluids employed have a share in the production of the coloring matter precipitated, it may seem immaterial which of the two precedes the other; I have, however, succeeded best by first injecting the prussiate of potass, the muriate of barytes, and the colored solution of cochineal, and afterwards the solutions before-mentioned adapted for precipitating each respectively. Very little force is to be used, and time allowed for the fluid to penetrate every part; this is especially to be observed in injecting the second or precipitating fluid, which . cannot be well done too slowly. If the part is intended to be preserved, a common minute injection made of size colored

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at least the appearance could not probably be explained in any other way. The most vascular parts of the cornea then seem to lie immediately under the membranes which cover its two surfaces, whilst its central part is apparently much less furnished with vessels. Mr. Astley Cooper, to whom I took the liberty of sending a specimen, suggested that the coloring matter might be rather supposed to be lodged in the vacuities of the cellular texture, and this opinion is highly probable. I have, however, been ready to believe, that, with a proper light, (not transmitted, but falling obliquely from above,) I have seen the vessels by the aid of a high magnifier; but I do not vouch this for certain, and it will be understood that wherever the vascularity of a part is mentioned in this paper, it is inferred from the color it has acquired from the injected fluid, not that I have seen the vessels themselves. I must leave it to others who have better means than myself to decide if this inference be correct. The capsule of the lens is supposed to be composed of two lamina, one proper and internal, and another external, formed of a reflection of the hyaloid membrane; between these two there probably lies a plexus of vessels, which send off numerous exhalents, that penetrating the internal lamen, secrete the humor of Morgagni: these are inferences I have drawn from having repeatedly seen the capsule injected or colored, and the humor of Morgagni stained and more abundant than usual. With respect to the lens itself, there is certainly a vascular connexion between it and its capsule, if not all over its surface,* at least at its circumference; once I imagined I had injected its external coat, I have many times seen it colored, but could always account for this by supposing that the coloring matter was rather deposited on, its surface from the humor of Morgagni. It is however pro

{>er to observe, that in no case whatever have I seen it coored internally, though my experiments have been particu. larly directed to this object.

The hyaloid membrane I have many times seen colored irt a greater or less degree, and am decidedly of the opinion, that in the adult state at least it derives all its vessels from the great arterial communication, situated a little behind the ciliary ligament, and not from the retina, as usually stated: my reasons for this opinion will be best stated when I speak of the retina; in the mean time I shall merely relate what

* I have twice observed after injection the capsule of the lens adhering so firmly to the tunica arachnoidea, that one could not be re-t moved without the other; the humor of Morgagni in these cases was of course wanting, though there was no appearance of disease.

has

has occurred at different injections. The anterior part was in general much more highly colored than any other, especially the strias, situated over the canal of Petit, where this membrane is connected with the ciliary processes. In one instance, after using the muriate of barytes, a portion of this membrane, reflected internally to form its cells, was seen beautifully injected; it bad much the appearance of the zigzag fracture in a piece of crystal, and extended in a direction from the edge of the capsule through the centre of the vitreous humor towards its posterior part. In this case the injection had failed in every other part, so that it was elsewhere quite transparent. The vitreous humor itself I have occasionally seen tinged.

The retina, as before observed, is chiefly supplied by its own artery, which however has communication at its anterior part with the general vascular system of the eye. It is known to be composed of two lamina; an internal one, consisting of little more than a plexus of vessels, and an external one, very analogous to the medullary substance of the brain. I have succeeded twice in injecting this part of the eye with the muriate of barytes; there did not appear to be the least communication whatever between it and the vitreous humor, but its vessels seemed to terminate almost entirely in its external or medullary coat, under the form of innumerable penicilli, which, from their proximity to one another, appeared almost to occupy its entire substance. It may here be observed that, probably owing to the injection escaping by exhalents, the prints of the vessels of the retina could be plainly traced on the hyaloid membrane, but they could be easily washed off with a little water, and thus evidently did not enter its substance: it is probable, therefore, that the artery of the retina exhales afluid between it^nd the hyaloid membrane; nothing, however, like the central artery* running from the retina through the vitreous humor to the capsule of the lens, of which so nfuch has been said, was ever perceived; I believe, therefore, that in the adult state at least, it has no existence.

All the above observations are to be understood to have been made upon the eye of the ox: those of an individual" not too old should be chosen; and I may here mention a curious circumstance, viz. that with those eyes which looked remarkably fair, and in which the cornea was unusually

* Since the above was written I have procured the eyes of a young calf, in one of which I thought I could trace the remains of the central artery; but as nothing of the kind was perceivable in the, other, I am inclined to believe it was only an accidental appearance.

transparent,

transparent, I have uniformly never succeeded; sueTf ey«fifhave a distinct character, by which they are easily distinguished, and of which the above-mentioned are the prominent traits; but I am totally unable to account for the fact.

Such are the chief remarks I have to offer on that part of the vascularity of the eye named by Bichat the capillary; and, though their utility may be called in question, yet they may perhaps afford at ieast amusement to the curious, and induce him to pursue thein. Should this not be the case, I may possibly at my leisure resume the subject, and communicate the result of some experiments already performed, and- of others intended to be made, with the view of ascertaining" the functions of some parts of this important organ.

To the Editors of the Medical and Physical Journal.

GENTLEMEN,

MY respectful acknowledgment is due to your correspondent Mr. Aber, for the reference he has given me, in the last Number of your Journal, to Mr. Barrett's publication on the analogy subsisting between Hydrophobia and Gastritis. In that publication, as Mr. Aber truly observes, I have been certainly anticipated, both in my theoretical and practicalfspeculations on the subject. It is indeed possible that the remarks alluded to may at the time have been read by me, but I have most assuredly not the smallest recollection of that having been actually the case. At that period, however, the perusal would not have probably made any very strong impression on my mind, as neither direct nor analogical experience had then afforded the subject the degree of interest in my estimation which subsequent occurrences have since given it. Although Mr. Barrett's observations, if ever known to me, had totally escaped my remembrance, yet it is still conceivable that they may have furnished a clue for noticing the resemblance which appeared to me to obtain between Gastritis and Hydrophobia. Of the" latter disease I Have had no practical knowledge, but the ample details given of it by other medical observers, enabled me to liken it to the appearances presenting in Gastritis, and seemed to warrant me in inferring, from the apparent similitude between the two diseases, that considerable similarity' of cause must also necessarily exist to produce such corresponding effects. Mr. Barrett, in his publication, rests the supposed resemblance between Hydrophobia and Gastritis on the morbid appearance in the oesophagus, and in thecardiac portion of the stomach, discovered by dissection, in

the

the former disease. My views on the subject arose from the symptoms and treatment of the latter affection; Mr. Aber has therefore justly observed, that Mr. Barrett's paper is the more valuable of the two. The deficiency of my speculation seems to have been abundantly supplied by the comprehensive statement of facts in Mr. Barrett's narrative. The practical induction too, as to the most efficient remedy, that of copious bleeding, is circumstantially proposed and enjoined by Mr. Barrett. Had I been aware of Mr. Barrett's paper on the subject referred to, it would have afforded me infinitely more gratification to have supported his judicious opinion by my experience of the advantages of bleeding in Gastritis, and by my persuasion of the correctness of the alleged affinity between the two diseases, than to have offered to the attention of the public observations that were much too crude and incomplete to be entitled to unqualified admission.

The coincidence that has occurred between Mr. Barrett and myself, is perhaps fortunate for the farther investigation of the subject. It may have the useful effect of bringing the question again into discussion, and of obtaining a stock of facts and observations that may be conclusive on the merits of the inquiry. On no other occasion has bleeding ever by my direction been carried to the length that it was in the case of Gastritis > formerly recited, and the ultimate success of the treatment in that instance appeared to be closely connected with its frequent repetition during a short period. In my judgment, it would appear to be a good general rule in, inflammatory affections, to draw blood not as is most commonly done daily, or twice a-day, but to repeat it every two or three hours whilst indicated by either morbid tone and hardness of vascular action, by inordinate visceral excitement, or by acute pain. The object in extensively deple-, nishing the vascular system, is to lessen the stimulus of distention, and to diminish the contractile power of the muscular fibre to a degree that would incapacitate the inflamed parts for sustaining the inflammatory action. This effect cannot be accomplished by insufficient means; the cause must be equal to the desired effect. The course of antiinflammant bleeding, that should be instituted in diseases like Hydrophobia and Gastritis, should be limited only by that degree of vital energy that would be secure against the extinction of life. Within this limit much freedom may be safely taken. When an evacuation of blood has rendered the action of the heart slow and feeble, even to deliqiiium, it will be discreet to desist, though indeed in this prudential forbearance nature commonly anticipates what is necessary

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