unfold the creases in its walls, the globule behaving as you might expect a bladder half full of water to do if you stepped firmly upon its centre; on continuing the process, however, no rupture of the walls could be detected, the contained fluid appearing to rapidly transude through its former envelope, which, on the needle being removed, collapsed to perhaps half its former size, and presented the aspect of a loose bag, almost without coloured contents, surrounding the nucleus. These changes were also examined under the -inch objective, giving a power of almost 1200 diameters, by adjusting its component lenses, for a covering glass slightly thinner than that actually employed, and then cautiously screwing down the objective, so as to compress a blood disk beneath it; under this finely graduated pressure and high magnifying power, the apparent expanding of fold after fold, in the plicated wall of a perviously wrinkled corpuscle, became strikingly evident. After tinting the external portion of the red disk with aniline solution, and then applying considerable force to the covering glass, either by means of a mounted needle under a low power, or, with the extremity of a high objective itself, so as to empty out all the hæmatocrystallin, the shrivelled envelope could be traced after the removal of the pressure closely applied to the surface of the nucleus, and under such circumstances occasionally presented an obscurely granular appearance.

Sometimes a few of the corpuscles situated near the edge of the thin glass, and therefore most exposed to the action of the air, appeared, after three or four hours, to become cracked in various places from the circumference to their centre; those fissures seem to involve not only the cell contents, but also the supposed cell wall; although at first sight this phenomenon may be deemed inconsistent with the older theory, in regard to the structure of the red disk, yet I think that it can be explained by supposing that the hæmato-crystallin had in these cases undergone a sort of troubled crystallization, causing it to form a mass of tolerable firmness, which split into fragments as it became dry, and at the same time cracked its membranous envelope, just as a piece of muslin frozen fast to a lump of ice is sometimes broken with the fracture of the surface to which it is attached. In some instances, the delicate and transparent cell wall could be detected in the flaw of the hæmato-crystallin, its outer edge showing a concave line across the peripheral extremity of the fissure.

The addition of water to the fresh blood gave very interesting results, and occasionally afforded an admirable proof of the existence of a membranous envelope. The first effect of diluting the liquor sanguinis was to increase the thickness of the corpuscle, and under its further action the disk gradually became less elongated, until it assumed a spheroidal form, the coloured portion being

rapidly dissolved out, and leaving the nucleus and cell wall more distinctly visible. In one instance, a corpuscle which had become quite decolorized attached itself to some little mass of granular matter, so that it could be retained under observation while I set up currents beneath the cover by tapping the latter with a mounted needle. On changing the direction of these currents so as to strike the disk upon various parts of its surface in succession, I was enabled to satisfy myself conclusively that it possessed a bladder-like cell wall, perfectly flexible (now that it was no longer distended with hæmato-crystallin), and capable of being dimpled in, as it were, by the force of the current impinging upon any side until it applied itself accurately to the subjacent surface of the nucleus, thus furnishing strong evidence against the doctrine of a sponge-like stroma (or oikoid), as taught by Brücke and Stricker, being a constituent of the red blood corpuscle.

If water was allowed to flow in upon a specimen, whose disks had undergone the curious crystallization above described, diluted liquor sanguinis seemed to rapidly enter the corpuscles by endosmosis, and dissolved the contained crystals which generally assumed a foliaceous appearance, such as we often see crystals of triple phosphate put on, when macerated in alkaline urine. As the hæmatocrystallin dissolved, the natural colour of the corpuscle was restored; its walls, if they had been previously propped out upon the points of the crystals, reassumed their normal shape, and in some instances these shortened or broken crystals were observed to move freely in the cavity between the nucleus and the cell wall.

Before attempting to make any deduction from the above experiments upon the blood of the Menobranchus, it may not be amiss to refer briefly to the views entertained by most German writers in regard to the red blood corpuscle. According to Rollett, in Stricker's 'Handbuch' above referred to, p. 296, Hensen was led, from the apparent retraction of the cell contents from the membrane as seen in the blood corpuscles of reptiles, to ascribe to the red disks a protoplasm which, accumulated especially around the nucleus and over the inner surface of the envelope, was bound together by delicate radiating crossed threads, and in its interstices contained the coloured liquid cell contents (gefärbte zellflüssigkeit); but in the opinion of Rollett, this thing is untenable in view of the knowledge we have lately obtained in regard to the properties of protoplasm, from the researches of Max Schultze and Kühne.

Brücke, who has observed these appearances after the action of a 2 per cent. boric acid solution, pictures to himself in explanation thereof, in the first place, "a porous form element, consisting of a motionless, very soft, colourless, and perfectly transparent substance; further, he represents to himself the body of the corpuscle as composed of a living organism, whose central portion forms the

nucleus of all nucleated red blood globules, and is free from hæmato-globulin, while the remaining portion contains the entire mass of the latter. The last-mentioned part Brücke considers as lying in the interspaces of the porous mass, filling them completely, but at the same time forming a continuous whole with the nonpigmented portion. The colourless porous substance he calls. Oikoid, all the remainder he names Zooid; and considers that, by the partial or complete withdrawal of the Zooid from the Oikoid, the occurrence of the above-mentioned appearances is explained. Stricker himself believes in the Oikoid of Brücke, but calls the remainder of the corpuscle its body (der Lieb)."

Recapitulating now the facts which I have detailed, militating against the views of Flint, Beale, and Ch. Robin, who hold that the red blood corpuscles of mammals are homogeneous drops of a jellylike substance, we find first, that when human blood is diluted with pure water, the bi-concave disks in general gradually assume a bi-convex and finally a globular form, their coloured portion being entirely dissolved, sometimes in the course of a few minutes, while the transparent colourless constituent which retains the spherical shape is completely insoluble in water, even during the prolonged maceration of over thirty days; and second, that when a mass of desiccated corpuscles, such as occurs in a dried blood-clot, is washed with pure water, so as to remove all the hæmato-crystallin, the outlines of the compressed red blood disks may be readily detected on examination with a sufficiently high power; further, that in the red globules of the Menobranchus, which may be supposed to bear a more or less close analogy in their constitution to those of mammals, it is possible to analyze the corpuscle by separating the coloured cell contents from the colourless cell wall, either by puncture of the membrane, by crystallization of its enclosed fluid, or by pressure upon the corpuscle, forcing out its contents apparently through the pores of the membranous capsule in the same manner that quicksilver is strained by pressure through the sides of a buckskin bag.

In opposition to the theories of Hensen, Stricker, and Brücke, who consider the red blood corpuscles are made up of a colourless porous substance called Oikoid, and a coloured more fluid ingredient denominated Zooid, may be enumerated the following circumstances: -First, if, on the one hand, we consider that a porous substance of the definite bi-concave form, analogous to a disk of compressed sponge, exists, it seems impossible to account for this stroma assuming a globular shape when acted upon by water, since the full diameter of the sphere, when formed, is occupied by the least amount of distended matter, while the dimension, in which lay the greatest bulk of stroma previous to the addition of water, is actually diminished; on the other hand, any hypothesis that the porous

substance coalesces, on the removal of its hæmato-crystallin, into a jelly-like drop, is negatived by the fact that occasionally, as is also described by Professor J. C. Dalton, one side of a corpuscle, rendered colourless by water, fails to assume a convex form, being apparently sucked in by the other side, which becomes exaggeratedly convex, until the whole corpuscle resembles a bell, or more accurately a liberty cap, in shape, without any tendency to present the outline of a sphere. Second, the appearance of the specimens I have examined strongly indicates the existence of a dense membrane, thrown into folds around the extremities of projecting crystals, just as a loosened tent cloth would be around the point of a cane thrust against it from the inside; and further, the movement of the crystals, when partly dissolved, around the nucleus but confined within the corpuscle as described in the early part of this paper, both tend to show that the cavity of the corpuscle between the nucleus and the membranous envelope is quite unoccupied by solid matter. Third, the perfect freedom with which one side of the cell wall of a red blood globule from the Menobranchus when acted upon by water may float in until it touches the nucleus, and out again to its own place, will, I think, furnish conclusive evidence to anyone who sees it as I have done, against the existence of a porous substance which maintains the shape of the blood disk.

From these researches I therefore conclude that the older theory, which asserts that the red blood corpuscles of the vertebrata generally are vesicles, each composed of a delicate, colourless, inelastic, porous, and perfectly flexible cell wall, enclosing a coloured fluid, sometimes crystallizable, cell contents, which are freely soluble in water in all proportions, explains the physical phenomena presented by red blood globules far more satisfactorily than any other hypothesis which has hitherto been advanced; and, moreover, that the usual bi-concave discoid form of the corpuscles in most mammals, as well as the changes of shape which they undergo in fluids of greater or less specific gravity than the liquor sanguinis, becoming crenated in denser, and globular in rarer liquids, are such as to be perfectly explicable by the light of our present knowledge in regard to the laws of the exosmosis and endosmosis of fluids through membranes; the equilibrium of these forces being maintained in normal serum, and one or the other being rendered preponderant if the specific gravity of that fluid is disturbed.-Transactions of the American Medical Association.

VI.-On the Use of the Nobert's Plate.

By Assistant-Surgeon J. J. WOODWARD, U. S. Army.

I Do not think the question of priority as to the resolution of the nineteenth band of the Nobert's plate, about which Mr. Charles Stodder makes such warm reclamations in the March number of this Journal,* possesses in itself enough general interest to make it worth while for me to add anything to what I have heretofore written on this head. If, however, as seems very probable, the Nobert's plate is to be much employed in ascertaining the comparative defining power of fine objectives, it is important that those who use it should have some reliable means of knowing whether they have actually resolved any given band; and such loose ideas appear to be entertained with regard to the matter in many quarters that it seems not undesirable to offer a few remarks on the difficulties involved, and the best means of overcoming them.

The satisfactory resolution of the Nobert's plate is, as is well known, complicated by the readiness with which spurious lines make their appearance parallel to the real ones, and simulating them more or less closely according to the character of the illumination employed. This difficulty is greater with the higher bands than with the lower ones, and with oblique light is more deceptive than with central illumination.

Three criteria for distinguishing the spurious lines from the true ones have been offered.

The first is the unaided judgment of the individual microscopist, who is supposed to be able instinctively to distinguish the false from the true lines without any special help.

The second is the enumeration of the lines in a measured portion of the band, and the comparison of the results attained with the statements made by Nobert as to their real distance.

The third is a count of all the lines in the band supposed to be resolved.

With regard to the first of these plans I must continue to think that it is utterly untrustworthy, and that should it unfortunately be generally accepted the plate would cease to possess any value as a measure of resolution, for individual enthusiasm would lead many to suppose they had succeeded, when in fact they were provided with utterly inadequate means.

It may be granted that an observer who has many times effected the true resolution of any given band will at length have its appearance so firmly impressed upon his mind that he will recognize it whenever he sees it as he would the face of a familiar friend, but this

*P. 118.