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formed and incorporated in the animal fabric. On a former occasion I showed by direct experiment how some of the chemical changes by which the nutritive materials are prepared for assimilation constantly take place in the blood ;* and it can scarcely be doubted that the saccharine matter takes part in these changes. In this way we are able to account for the disappearance of some sugar from the blood during its transit through the lungg, without being compelled to believe that the transformation depended on any peculiarity in these organs or in their contents. The theory of the disappearance of saccharine substances from the general circulation seems, as far as science has yet advanced, to be equally supported by reason and confirmed by fact ; and although future research may cause physiologists to modify this opinion, we can never be blamed for having deduced it from the data which we at present possess.

Art. II. On the Epithelium of the Air-vesicles of the Human Lung. By C.

RADCLYFFE HALL, M.D., F.R.C.P.E., Physician to the Torquay

Hospital for Consumption, &c. In a series of papers on the pathology of pulmonary tubercle, published in former numbers of this Review, t I endeavoured to show cause for concluding that in such cases of chronic pulmonary consumption as do not originate with actual inflammation, fatty atrophy of the epithelium of the air-vesicles is a condition antecedent to the formation of tubercle. It would, of course, be fatal to my argument if it could be proved that in health there exists no such thing as an epithelium at all upon the walls of the air-vesicles.

In the number of this Review for October, 1855, Mr. Rainey enters at some length into the “Critical Examination of the Evidence for and against the presence of Epithelium in the Air-cells of the Human Lung," and arrives at the conclusion which he had previously held, that there is no epithelium in the air-cells. From his acknowledged reputation as an accurate microscopist, any conclusion of Mr. Rainey on such a subject carries considerable weight; and those writers who dispute the existence of the epithelium referred to, do so mainly in deference to his authority.

Before proceeding further, I owe it to Mr. Rainey to apologize to him for an unintended misrepresentation of one of his statements. In my first paper it is stated—“Blood corpuscles, seen throngh the walls of the capillaries, were indicated by Mr. Rainey as having possibly been mistaken for epithelial cells." What I ought to have written was—“Nuclei seen in the walls of the capillaries," &c.

Mr. Rainey's arguments against the existence of the epithelium may be summed up under the four following heads: (1.) The negation on some good anatomists. (2.) The discrepancies in the descriptions given by those who affirm the existence of an epithelium in the air-vesicaces

• April and Oct. 1855 ; and April, 1856.

y or Respiration in the last October number of this Journ

+ See & review of the Chemistry of Respiration in the last October

(3.) The real explanation of the appearances which the affirmers have mistaken for epithelium. (4.) The evidence of comparative anatomy.

The first head, involving merely a question of relative authority, needs no further comment than the remark, that the positive evidence of one trustworthy observer is usually allowed to overrule the negative evidence of many.

Under the second head, Kölliker is referred to as stating that the epithelium of the air-cells is difficult to demonstrate in situ, but as making no allusion to the want of distinctness or completeness of its individual cells, but, on the contrary, as actually giving their admeasurement; whilst I, on the other hand, am stated to make no mention of any difficulty in finding this epithelium in the lung, but to describe its individual cells as wanting that distinctness of outline and regularity of form which characterize other epithelia. From this diversity in our descriptions, Mr. Rainey infers that “there is every reason to conclude that the epithelium mentioned by Kölliker is not the same as that described by Dr. C. Radclyffe Hall.” Surely this is little more than special pleading; particularly when Dr. Thomas Williams and myself are admitted by Mr. Rainey to have described the same thing, and in the main to agree in our representation with the delineation given by Van der Kolk.

Under the third head, the appearances which Mr. Rainey considers to have been erroneously supposed by myself, and others of higher authority, to represent pavement-epithelium, are referred to (a.) "imperfectly developed epithelial cells from the smallest bronchial tubes, which had been detached in the process of manipulating, and had got by accident into the air-cells. This is so common au occurrence, that such corpuscles are generally found in greater or less quantities in these cells; but they have not the most distant resemblance to pavement epithelium, as seen in other parts of the body, nor to the imaginary hyaline pavement-epithelium represented in Van der Kolk's plate, and the greater part of those described by Dr. R. Hall, which in most respects agree with the latter.” If they do not resemble what we have described, why suppose we have seen one thing and described another? (6.) Nuclei belonging to the walls of the capillaries, both those capillaries which project and those capillaries which are so blended with the membrane of the air-vesicles as not to present a distinct outline in the uninjected state. The italics are mine. It must be difficult to decide that the nuclei really belong to the walls of such capillaries as cannot be seen in the uninjected state. Considering the extreme minuteness and delicacy of the air-vesicles, how is it possible to conclude that such nuclei do not belong to the wall of the air-cell rather than to the wall of a capillary which is invisible until the lung has been injected ? (c.) Oval spaces bounded by meshes of capillaries. (d.) The sharp threads of elastic tissue, also, have “a part in producing the confused epitheliumlike appearance in the air-cells."

In support of his views, Mr. Rainey depends chiefly upon his examination of injected lungs. I have never been able myself to find epithelium in the air-cells of an injected lung, for the obvious reason that I have never yet seen a specimen in which sufficiently high powers of the microscope could be employed for the purpose. In order to examine an object so fine as this epithelium is, the air-cell must be used as a translucent object, and must be very carefully prepared to be distinctive even in that condition.

Mr. Rainey speaks throughout as if one type and size only of pavement-epithelium were possible in the various structures of the body. We are not, however, tied down to any such supposition. If we find fine flattish nucleated plates lining an air-cell in a tesselated fashion, we have a right to designate them a pavement-epithelium, however greatly they may differ in size or regularity of shape from the typical pavement-epithelium elsewhere.

The arguments adduced by Mr. Rainey from comparative anatomy appear to be open to exception. For example, when Mr. Rainey states that in insects many of the trachexe are so remarkably minute that “there can be no room for pavement-epithelium,” there seems to be no absolute reason why an epithelium correspondingly minute might not exist. Moreover, if this be an argument against the presence in mammalia of an epithelium in the air-vesicles, it would be a still stronger analogical argument against the existence of the much larger bronchial epithelium, which no one disputes. But, as William Pitt is said to have remarked in reference to Butler's great work, "you may prove anything by analogy!

Finding nothing in Mr. Rainey's observations to shake my conviction, founded ou long-continued use of the microscope, upon the sub

ject, I requested my friend Dr. Brittan, of Clifton, to read Mr. Rainey's paper carefully, and then to favour me by investigating the question afresh. I now publish the result of his examinations, merely adding one illustration of my own.

In examining the specimen from which the adjoining drawing was taken, the various possible sources of mistake pointed out by Mr. Rainey were severally borne in mind. I think the appearances, which I have here represented as faithfully as I was able—and Mr. Bagg, on his part, has done justice to the drawing-cannot

be referred to any of them, or to any. Fig. 32. Appearances seen in airvesicle of kitten's lang whilst yet warm and moist, previously inflated 1 inch ; this object became more indis

pavement-epithelium. The indistincttinct in a few minutes, whilst under ness which so soon came on, and to examination.

which Dr. Brittan afterwards alludes, was probably due merely to the drying of the specimen whilst under examination.

• The figures are numbered in continuation of those in former papers in this Review.

In assenting to my request, Dr. Brittan* stated that he had hitherto never made the point one of personal investigation, but that, so far as his impressions went, he was inclined to agree with Mr. Rainey. I proceed to quote from Dr. Brittan's subsequent communications, employing his own language, though not intended by him for publication ipsissimis verbis :

“1. In a Toad.I did not find much ciliated epithelium ; but I satisfied myself of the presence of an epithelium in the pouches, and, I thought, over the ridges likewise. There was, however, nothing very clear—nothing one could have drawn.”

“2. A Frog.—Ciliated epithelium very evident and plentiful ; epithelium everywhere evident.”

“3. Sheep.—There were in this specimen a profusion of small entozoa, and the bit of lung seemed much altered, as if from small effusions of fibrin,much like what you describe. I convinced myself of the presence of epithelium, however, after examining many portions."

“4. 08.— A bit of fresh lung from the ox settled the point for me. When I had properly prepared the specimen, the epithelium was as plain to me as it could be; and I am satisfied none of the errors ascribed by Mr. Rainey applied here. The appearance of the cells is not analogous to that of the nuclei in the capillaries; they are to be seen all over the wall of the air-vesicles, sometimes in a continuous layer; whilst close by will be a portion of the wall without these cells, or with only a few scattered here and there still adherent. I cannot, therefore, be misled by the appearance of the fibres of the pulmonary tissue. It certainly was not bronchial epithelium, for I carefully removed a portion of the latter for comparison. I have no hesitation in saying that in this lung the vesicles were lined by epithelium. I send you a slight drawing of this specimen, in two aspects, one focussed on the top, the other a little deeper.”


Fig. 33. From the lungs of an ox (Dr. B.). No, i is the same specimen ag No. 2, but in

different focus, showing prominently the edges of the air-vesicles. Physician to the Bristol Royal Infirmary, and Lecturer on the Practice of Medicine at the Bristol Medical School; formerly Lecturer on Anatomy and Physiology.

No. 3. Cells separately drawn from No. 2: these were drawn as they appeared seen by the 1-12th.

Fig. 33 2. From the lungs of an ox. No. 2 is focussed

down to show the sides or floor of air-vesicles.

5. Sheep.-In this specimen of sheep's lung I found the epithelium as plain as plain could be. Two or three flakes of it lying at the edge of the specimen, afforded beautiful specimens of a single layer of tesselated epithelium.”

“6. Kitten.—I examined the lung of a kitten quite fresh, and found the same, nor did I observe the change (of early becoming indistinct) to which you refer. In fact, the specimen shows almost as well now it is put up in spirit and water as ever it did.”

"7. Human Lung.—This specimen was not sound, being taken from an emphysematous lung from a patient who died this morning. The epithelium seems, as described, much less firm and more hyaline? than in any of the other specimens which I have examined. On putting up a specimen, I find only scattered cells in great quantity all round in the fluid, sometimes six or eight or more together, and a few still adhering; but on the surface of the specimen they are plainly distinguishable. I have not the slightest doubt about them, nor had Etheridge, who happened to come in ; but there was nothing evident enough to be worth drawing. Of course, one would hardly expect the same condition in the lung of a patient thus diseased, as in that of an animal killed in health and vigour."

"8. Human Lung.—The specimens I examined from this were decisive to me. I compared them with a specimen of bronchial epithelium, and also with a bit of peritoneum with its epithelial coat still on, and I really cannot see how any one who has worked up the subject by making specimens for himself can entertain a doubt. Considering the scepticism expressed in my first letter to you, the certainty I now express is pretty strong, but so much the more trustworthy; and I am really obliged to you for having made me take up the subject and satisfy myselt. I ought to have mentioned to you that I have remarked in the epithelium in question that the nucleus appears to be

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