Mineral acids, if dilute, do not dissolve the corpuscles ; if concentrated, dissolve them completely. :Caustic alkalies form a jelly with them ; their carbonates, as also muriate of am monia, change them similarly but more slowly. The action of the latter on pus was observed by J. Hunter on a large scale, and ascribed by him to coagulation of the liquor puris. Dr. J. Davy showed, by allowing the corpuscles to settle, decanting the supernatant fluid, pour ing some of the muriate upon this, and observ ing that no viscidity followed, until corpuscles had been added, that the change depended upon these. Dr. Wood -I. ascertained that the muriate causes the corpuscles to adhere with some closeness to each other.
Pus-corpuscles contain a very little phos phate of lime, and consist essentially of a pro tein-compound. Their constituent substance has been given the special title purium by Koch, purulina by Michelotti ; a mode of naming it which must be abandoned if', as Lehmann and Messerschmitt maintain, the nu cleus and involucrum belong to two different varieties of protein,— the former being com posed of venous, the latter of arterial, fibrin,t But this view is, it is scarcely necessary to add, itself far from being established,—as also that of persons who (imitating Ascherson) hold the centre of the nucleus to be composed of fat, and its peripheral part of albumen.
Pus differs chemically from blood in the states of health and of hyperinosis in the proportion of its ingredients, much more than in their nature --as might readily be imagined. But quantitative analyses are as yet so imper feet, that very different general inferences may be deduced from thern according to the selec tion made of published analyses; — it is true this may also in part depend on the actual vari ation in the proportions in different specimens of pus. Thus we may prove by one set of experiments that pus contains more water than healthy, and ci fortiori than hyperinotic, blood ; and, by another, that pus is on the contrary a more concentrated fluid than either. And whichever be the opinion adopted, theoretical explanation and support may readily be found for it. The follovving general inferences are likewise, we confess, to be accepted with caution.
Pus contains more albumino-fibrous sub stance than the liquor sanguinis of either spe cies of blood, less than the blood in mass, com prising the red' corpuscles. The latter point obviously depends on the fact that the cor puscles are, as such (unless accidentally and in very minute proportion), retained within the vessels ; whereas pus is formed outside them. But how comes it that pus contains
proportionally, more albutnino-fibrous material than the liquid part of the blood — that part of the blood which is exuded in inflamma tion, and which forms the substance for the evolution of the purulent matter ? The pecu liarity (as suggested by Lebert) is probably due to partial solution of the red-corpuscles in the liquor sanguinis, and transudation of that dissolved substance ; an explanation not, xve may observe, without apparent connection with the established fact of the decrease of red corpuscles in hyperinotic blood. To this source (as well as to extravasation) may, perhaps, be referred the occasional appearance of a little iron among the elements of pus.
Fat is much more abundant in pus than in blood ; the high ratio of cholesterin in the former (as ascertained by Valentin *, Von Bibra and Wright) comes in confirmation of the fact established by Becquerel and Rodiert, that the ratio of cholesterin in the blood is always in creased in inflammation. The saline consti tuents of the two fluids do not differ very materially.
Pus possesses a remarkable power of re sisting decomposition ; at the end of months some corpuscles may still be found unchanged, among others that are dissolved. It even re tards the putrefaction of substances with which it is brought in contact, as shown by the experiments of J. Hunter and Everard Home. The latter observed that pieces of flesh placed in fresh pus underwent gradual dimi nution of weight, and eventually solution, without any evidence of putrefaction being manifested. Ultirnately, pus does putrefy however ; the occurrence of the change being much hastened by the presence of blood, mucus, or other organic fluids. Acidity, as already hinted, is one of the earliest signs of the change.
The various appearances of pus have given rise to its classification into the creamy, curdy, serous, and slimy varieties (Pearson); one obviously unfit to represent the existing state of knowledge. It seems better to con sider pus as of two kinds : I. Simple ; II. With added characters,—the added character being derived either from (A) Substances of known nature, natural or morbid ; or from (B) Sub stances of unknown nature, called viruses.