No product of disease has, perhaps, been the subject of such zealous research as pus and ichor, and yet nowhere has a greater number of shortcomings been overlooked or glossed over than here. These we may be incompetent to remedy; we may, however, render some slight service to pathology if we can succeed in simply directing attention to them.

There are so many kinds of purulent-looking fluids, and there is so great an affinity of these fluids amongst each other, that, for the sake of discrimination, it is indispensable to establish one standard form of pus. Such a standard form is furnished in the pus of granulating, healing wounds, as well as in that of certain abscesses.

This normal pus is a homogeneous, cream-like, fatty, glutinous fluid, of a yellowish color, of a flat, sweetish smell and taste, of a specific gravity of from 1030 to 1333 (Vogel), and when recent, of alkaline reaction.

It consists essentially of pus-serum, with certain form-elements, these being, besides molecular granules (elementary granules), the pus-nucleus, and the pus-cell. To these is to be added the pus-placenta, of which more hereafter.

The pus-cell is a spherical or oval - now smooth and even, transparent, thin membraned - now granulated and opaque, nucleated cell, which, under a magnifying power of 400 diameters, appears colorless, or faintly yellow, and measures from 1/100 to 1/60th of a millimetre in diameter.

Its granulated nucleus, firmly attached to the cell-wall, is, in the translucent cell, visible without the aid of artificial expedients. In the granulated cell, on the contrary, it is rendered indistinct, if not totally obscured, by the contents of the cell, but is readily discernible on the application of acetic acid. It generally occupies from one-half to two-thirds of the cell's cavity, and in rare instances almost fills it up. Generally speaking, it is single; not unfrequently, however, it is manifestly composed of from two to five smaller corpuscles. Normal pus only rarely contains larger cells, with two, three, or four nuclei. Under the action of acetic acid, each pus-nucleus being brought out with sharper contours, as a spherical (according to Vogel, cupped) body, presents the well-known characteristic phenomenon of indentation and eventual splitting. In other words, the nucleus, after passing through sundry modifications of shape, down to that of a trefoil, finally breaks up into two, three, or four sharply-defined corpuscles, no further soluble in acetic acid.

Besides the cell-inclosed nuclei there are present free nuclei. These are in like manner either single (perfected), or made up of from two to five corpuscles, and they exhibit the same phenomenon of indentation and splitting, when treated with acetic acid.

The molecular granules are present in various numbers, some scattered, others grouped together.

The contents of the cells are in some cases -limpid, in others, owing to very minute granulations, nebulous. It is very common to find one compact group of pus-cells presenting every known gradation in the quality of their contents.

The development of the pus-cell is easily demonstrable, falsifying the assertion that the nuclei are artificially produced by chemical agency. For the most part from two to five of the larger molecules associate themselves into a group, and constitute, thus aggregated, an imperfect nucleus. By and by they coalesce, and present a simple, finished nucleus - a fabric reducible, by the agency of acetic acid, to the very same elements.

The nucleus now becomes surrounded, often immediately, with a cell wall, so closely fitted at first, as to require the endosmotic agency of water, or dilute acetic acid to disconnect it, and render it cognizable. Many nuclei, however, become previously endued with a delicate nebulous deposit, which by and by puts on a circumscribing cell-envelope, and assumes the contour of the cell.

These formations are, to a greater or smaller extent, always discernible in genuine pus, in the progress of germination.

Cells devoid of nuclei, - clear, transparent cells, which have to create a nucleus out of their own materials, are rare.

The phenomena of endosmosis and exosmosis bring out the pus-globules with great clearness.

The chemical relations of the pus-cell are not without their weight in reference to its constitution, and to its recognition.

Dilute acids, for example, dilute hydrochloric, oxalic, tartaric, but especially acetic acids, have the effects of tumefying, loosening, attenua-ting, bursting, without entirely dissolving the pus-cells, whilst upon the nuclei they produce the above-mentioned appearance, first, of greater distinctness of outline, then of indentation, and lastly, of disruption.

Caustic alkalies and their carbonates convert the pus-cells into a jelly-like, granulated substance.

Thin solutions of certain saline substances, as for instance, of chloride of sodium, hydrochlorate of ammonia, nitrate of potash, iodide of potassium, with many others, cause first the disappearance of the sheaths, and secondly, the swelling up of the nuclei into a shapeless grume.

A solution of borax acts like the alkalies, only less rapidly. Metallic salts, alcohol, tannic acid, etc, which coagulate fluid albumen, render the pus-globules shrunken, nebulous, and opaque.

In the blood, in urine, in mucus, and in saliva, the pus-cells are preserved unchanged; bile, on the contrary, occasions a disappearance of the sheaths, and a bloated aspect of the nuclei.

From these facts, and from further experiments in the same direction, Lehmann and Messerschmidt draw the following conclusions:

1. The sheath of pus-cells, turgescent in acids, soluble in solutions of caustic alkalies, and of their saline conjunctions, is identical with a protein-compound which may be artificially produced out of albumen, deposited by water, and redissolved by alkaline salts, and acetic acid - a modified albumen, poor in salts, constituting a transition stage to fibrin - fibrin a.

2. The nucleus, insoluble in acetic acid, soluble in solutions of alkalies, turgescent in solutions of salts, a protein-compound similar to the venous fibrin, turgescent in salines - fibrin b.

3. The third substance, namely, the molecules accompanying the pus-cells, forming part of the contents of the opaque granulated cells, and even exhibited in the nuclei (the nucleus-corpuscles of Lehmann and Messerschmidt), are uninfluenced by alkalies or borax, and are regarded by Lehmann and Messerschmidt, as a substance analogous to the essential constituent of horny texture. They, however, partly consist, as Vogel rightly maintains, of fat.

Besides these elements, pus not unfrequently contains cholesterine-crystals, crystals of ammonio-phosphate of magnesia, animalcules, etc.

Like Henle, we have been unable to satisfy ourselves of the above-mentioned effect of alkaline salts or of borax solution. In the changes wrought by the application of thin solutions, we recognize the phenomena of endosmosis down to rupture of the sheath of the pus-cell; in the changes wrought by the application of saturated solutions, a shrivelling thereof.

The pus-serum in which, when at rest, the pus-cells gravitate, has the composition of blood-serum, with some difference, however, in the relative proportions of its constituents; fat, for example, predominating. With respect to pyin, to which we shall afterwards have to recur, our belief is that it is not a constituent of normal pus at all.