PURULENT DEPOSIT, OR PUS• Pus is a fluid of whitish-yellow or greenish colour, and homogeneous aspect ; of faint, pe culiar smell, when warm ; inodorous, when cold ; of creamy consistence ; and of sweetish, or sometimes saltish, taste.
Pus consists of a liquid part (liquor purls) holding in solution organic prinoples and in organic salts ; and of a solid part (corpuscles) held in suspension in the liquor puris. These constituents separate spontaneously, after re moval from the body, with a degree of slow ness increasing. as the purity of the pus ; when the liquor purls is in excess, the corpuscles sink rapidly. The corpuscles are not sepa rable from the liquor puris by filtration. Pus does not naturally contain gas of any kind (J. Davy). Its specific gravity ranges between 1042 and 1021, the weight most commonly observed being about 1030.
Four kinds of organic corpuscles are found in pus : (I.) Proper pus-corpuscles ; (2.) Py oid corpuscles; (3.) Granules ; (4.) Compound granule-corpuscles.
(1.) The proper pus.corpuscle is a body of tolerably spherical outline, unless when acci dentally flattened or otherwise altered in shape by the pressure of adjoining corpuscles ; its edge, slightly dentated, as we have commonly seen it, may be perfectly even ; its surface finely granular-looking. The corpuscle is (commonly, but not always,) moderately trans parent, subjacent bodies being visible through it, as is particularly obvious when a weak iodine-solution has been added to the fluid. The diameter of the corpuscle varies from the to the 7711r,„ of an inch,—averaging about the „Irm. lts substance is somewhat elastic. It never, as far as we have seen, presents a narrow edge to the eye, in the manner of the red corpuscle of the blood.
The contents of the corpuscle are semi fluid and solid. The semi-fluid substance seems of slightly gluey consistence. The solid contents are the nucleus or nuclei. It was low, taught that if the pus examined be recent, and° chemically unchanged, the nucleus is not perceptible even with strong magnifying powers. This is now known to be erroneous ; we have, with a glass magnifying only 400 diameters, detected a nucleus in laudable pus of neutral reaction, immediately after removal from the body.* But, under the influence of dilute acetic
acid, the nucleus is more fully brought into view, and is seen dose to the cell-wall, in the form of a bipartite, tripartite, or quadripartite body (more rarely a single one), all the divisions of which lie nearly on the same plane side by side. Each division of the nucleus is smooth, circular, or slightly oval, and biconcave. The central depression, which exists as a conse quence of its biconcave form, either appears opaque, while the surrounding part is clear and transparent, or the former is transparent and the latter opaque,—ditierences depending on variation of the focus of the microscope. The surface of the nucleus is very finely granular ; its diameter varies from the ,A, to the 6 o,c,„ of an inch.
(2.) Under the name of ppoid, M. Lebert* distinguishes a corpuscle smaller than that just described ; spherical in shape, tolerably trans parent, rather of solid than liquid consist ence ; containing from four to ten granules or more in their interior, and wholly unprovided with nucleus, acetic acid simply rendering the corpuscle more transparent. These bodies, resembling most closely the cells of tubercle (p. 105), are larger and more spherical than these : so great is the siniilarity, that M. Lebert was at first led to consider the pyoid cor puscle peculiar to tuberculous pus ; but, sub sequently finding it (as we have also done ourselves) under circumstances excluding the idea of tubercle, has relinquished this notion.
(3.) The elementary granule seen in pus is of spherical shape ; it is never cupulated, so far as we have seen, and is less than half the size of the nucleus of the pus-corpuscle, ave raging the of an inch in diameter. These granules are obviously not, as was once maintained, detached nuclei floating in the liquor puris. They are either single and soli tary, or (less frequently) collected in irregular groups. Their composition varies, as they are sometimes soluble in mther, and sometimes exhibit the reactions of a protein-compound ; this chemical difference is not alv.ays con nected with any physical peculiarity, which the eye at least can detect.