first, because there were no large oval corpuscles, the red globules proper, but only the small circular ones; second, because they were fixed in the tissue, not floating to and fro in blood serum; third, because I had seen many of them migrate.

These phenomena were witnessed not by myself alone. Dr. Bridge, Lecturer on Practice of Medicine, observed the emigration of several corpuscles; Dr. Danforth, Professor of Pathology, while unable to watch the process for a considerable time, was convinced that emigration actually occurred; Miss Mergler observed numerous red as well as white cells leave the vessels.

Having established the fact of the locomotion, therefore, it remains to prove the dependence of that locomotion upon mechanical congestion rather than upon active hyperæmia. That congestion existed was shown not only by the retardation of the blood-current, and dilation of the vessels, but also by oedema of the web, which became evident within twenty-four hours. That the congestion was not "active" was established by two facts; first, the absence of all the phenomena of inflammation, other than the amoeboid movements-i. e. the primary acceleration of the blood-current, the subsequent retardation with irregular contractions of the vascular walls; second, that the discontinuance of the pressure on the vein was at once followed by complete restoration of the circulation in the web, whose irregularities, therefore, were dependent wholly on a mechanical impediment and not upon any "nutritive irritation," nor vascular spasm.

This experiment has been repeated twice since the above date. In both instances emigration occurred; in one it began within three hours after compression was made. In this case the pressure exerted exceeded somewhat that made in the first instance.

Now, the value of these facts depends upon one's ideas of pathogenesis. If he believes, with Billroth, that connective tissue is developed solely from migrated blood corpuscles, he has a key at once to the connective tissue hyperplasia of the skin and venous walls which accompanies a varicose condition of the veins. For the mechanical congestion necessarily present must result in the emigration of blood corpuscles into the surrounding tissues, and these are developed, says Billroth, first into spindle cells, and finally into complete connective

tissue corpuscles, causing the familiar thickening of the skin and vascular walls. In support of this view is the fact that the increase in thickness in the wall of a varicose vein is due to hyperplasia, not of the muscular elements, but of the connective tissue bundles interposed among those elements, and of the outer coat of the vessel which is composed wholly of connective tissue. So, too, the enlargement of the spleen which usually follows portal obstruction, as in cirrhosis of the liver, and the thickening of the superior hemorrhoidal veins-" hemorrhoids"from the same and other conditions, are to be referred, in part at least, to the development of leucocytes which have wandered from the vessels during the mechanical congestion. Perhaps, too, the areolar hyperplasia so often found with displacements of the uterus is due to the venous congestion which usually exists in that condition.

Even the conservatives like Stricker and Rindfleisch, while insisting on proliferation of pre-existing cells as the more important source of connective-tissue hyperplasia, admit the strong probability that a considerable part of it is due to the development of the wandering cells or colorless corpuscles first into spindle cells, then into fibrillated tissue. Certain it is that, in the repair of wounds, at least, they play a prominent part in the formation of cicatricial tissue.

The fact of emigration without any evidence of that "nutritive irritation" of tissue, which Virchow presumes in active hyperæmia, would seem to favor Hering's view that the exit of corpuscles is a passive rather than an active movement, due to their glutinosity, to increased blood pressure and diminished blood velocity-in short, a simple filtration of colloid sub

stances.

Then again the behavior of the small red corpuscles is interesting as exhibiting their close relation with the white, and as furnishing another link in the chain of circumstantial evidence that the red corpuscles are transformed white ones. Such has for some time been the prevalent opinion, though never completely demonstrated. The fact that these red ones were but little if any larger than the white, that they were of circular shape, were devoid of nuclei, and possessed the power of amoeboid motion, proves their close connection with the colorless cells; while the presence of hæmoglobin, as indicated by their color, testifies to their ability to perform at least one im

portant function of the fully-developed red ones, namely, the transportation of oxygen.

Upon further examination of the literature of this subject, I find in Wagner's Pathology (p. 186), Charlton Bastian cited as authority for the statement published in the British Medical Journal for 1868, that "red globules as well as white leave the vessels in venous stases, scorbutus, etc., by means of amoeboid movements." Not having had access to the Journal I do not know upon what observations he based his statement, nor whether he had made investigations similar to my own.

A NEW DEVICE FOR DARK-FIELD ILLUMINA

E

H

TION.

BY PROFESSOR WM. LIGHTON.

B

I HAVE been quite interested, lately, in some experiments connected with the subject of dark ground illumination, and have worked out a device which brings out new and most interesting results. The accompanying diagram will illustrate its working. Let A, Fig. 1, represent a sectional view of the tube of an eye-piece; B, a triple achromatic lens of one inch focus, and 30 degrees aperture; C, the diaphragm; D, cap of the eye-piece sliding over the tube of the achromatic lens; E, a thin brass plate sliding between grooves in the top of the cap, having at the point Fa small hole of not more thanth of an inch in diameter; H, the cone of rays of the achromatic eye lens, meeting at I. Place the thin plate so that the hole F will be at the side, and as near the apex of the cone of rays as possible. It is quite evident that none of the light usually used by the eye will be allowed to pass to it, as it will be

FIG. I.

interrupted by the brass plate. By placing the eye at the hole F, and looking at a suitable object upon the stage of the microscope, a most wonderful sight will be seen. The object will be brilliantly shown upon a dark field. I would suggest its trial upon the diatom Heliopelta. It is not necessary to explain the principle of the device, as it will be quite evident to those familiar with optical work. By revolving the eye piece in the body tube many curious changes in the appearance of the object will take place. In using oblique light it will be found best to place the hole on the opposite side of the cone of rays from the mirror. The arrangement can be used with the common eye piece, but with an inferior result. The value of the device can be tested by making a hole in cardboard with a small pin, and holding it at its proper place over the eye piece.

Ottumwa, Ia., Sept. 2, 1878.

[The principle involved in the above may not be seen at once by all our readers. A little thought will show that the object is not seen by transmitted light, but by that which it radiates itself; the direct light from the mirror being quite cut off.-ED.]

ON THE SPORE-FORMATION OF THE MESOCARPEÆ. A paper on this subject was presented by Dr. Wittrock before the Swedish Academy of Science last December and published in the Bihang till k. Svenska Vet. Akad. Handlingar, Band V. The publication is not accessible, so we cannot refer to the original (which is printed in English), but as the views advanced by the writer are worthy of more than a passing notice we do not hesitate to reprint the following from Nature.

In one lovely group of green-colored algæ we find a number of very pretty species, many of which consist of one-celled forms, and others of which, obeying a law of cell growth, not only produce new cells but also cause these to adhere to one another and so, as this growth goes on, give a chain-like or filamentous appearance to the mass. These filamentous green freshwater algae are very common. Dillwyn, in the beginning of this century, knew and described many of them, and he also seems to have well known that the contents of some of their cells formed oval bodies called resting spores. The merit of having worked out the history of these spores belongs to Prof. A. de Bary, from whose researches it was first made clear that in some of these forms (Zygnema) one of the chains of cells will come to lie alongside of another chain, and then the cell-wall of two opposite cells will grow out

wards until they meet. On meeting, the tips of these outgrowths will be absorbed, and the two cells will thus communicate by means of this newly-formed canal, whereupon it will follow that the contents of both cells will each go half way to meet the other, and their conjoining will take place in the newly-formed canal, or sometimes in one of the cells; or that the whole of the contents of one of the cells will pass over and combine themselves with the contents of the other. In either case the result will be the formation of a new body-well known as the zygospore, but also known under many other denominations. But, again, in other forms (Mesocarpus), while the initial process will be the same, so far as the formation of the cross channel goes, the further steps differ much, it being only the green-colored portions of the protoplasm of both cells that move over into the canal, whereupon the central portion of this green mass, composed of about equal parts of the contents of the two cells becomes developed into a zygospore, leaving the rest of the cell-contents to fade away. The physiological import of these two quite different phenomena was therefore this: in Zygnema and its allies the total contents of two of the cells were required to form a zygospore—whereas in Mesocarpus this was formed out of only portions of the cell-contents. There is thus no strict analogy between these two forms of zygospores, and they probably should not both receive the same name. De Bary perceiving this, referred to the one as resting-spores formed by the partition of the zygospore (the parts destitute of green contents having been partitioned off), strangely applying this term to that stage when the two cells had combined to form one, and to the other as resting-spores without partition. De Bary's attempt at being logical has apparently been overlooked by many writers on this subject, notably by such eminent investigators as Max Cornu and Sachs, who still apply the term zygospore to both forms, but Pringsheim has grappled with the difficulty in his most thoughtful paper "On the Alternation of Generation in Thallophytes," and suggests that the first stage in the reproductive proscess in Mesocarpus is the "conjugation" stage-here the cells join and become, so far as their cell-walls are concerned, united into one. The next stage is the more important one, in which the cellcontents commingle, and the result is the production of the central cell -a carpospore-and of two or four cells which surround it, and form the equivalent of a fruit-like body, or sporocarp, and of course it would make no matter whether this sporocarp were formed in the connecting canal as in Mesocarpus, or whether it fills this and extends over into both the cells as in Staurospermum, or as in Plagiospermum is altogether formed in one of the cells; the essential feature being the differentiation into the carpospore and its investing covering the spor

ocarp.

Now Dr. Wittrock has made the rather startling observation that in