and a sulphate, beside’traces of phosphate of magnesia, oxide of iron,
and vitrifiable matter (probably silica).
The different kinds of pus are next mixed with large quantifies of water, and the matter which subsides examined separately from the water. In the same manner they are next mixed with alcohol, and afterwards with acetic acid, but without any remarkable results. Dr. Pearson also made various attempts to discover a criterion by which to distinguish pus from mucus; but after trying the agency of sulphuric, nitric, and muriatic acids, he says he could by these dis- cover no constant characteristic property of these substances by such experiments.
By alkalies also, he was not more successful; nor did the subsequent addition of acids to the solution afford criteria which could be depended upon, as has been supposed by other experimentalists. After trial of several different neutral salts, he observed the same effect from sal-ammoniac which had been noticed by Mr. Hunter, and was considered by him as coagulation : but Dr. Pearson gives it the name of inspissation, and observes, that this effect is not pro- duced in expectorated matter by the same salt; so that this is un- doubtedly a criterion, as it was supposed to be by Mr. Hunter.
From the whole of his experiments, Dr. Pearson infers that pus essentially consists of three distinct substances : first, an animal oxide in the form of fine curdy particles, not soluble in water, not coagu- lable into one mass by hot water ; secondly, a limpid fluid, like serum of blood, and like it coagulabie by heat or by alcohol; and thirdly, innumerable spherical particles, visible only by the micro- scope, not soluble in hot or cold water, and specifically heavier than water.
He observes also, that other extraneous matters are sometimes mixed with pus: that whenever pus is fetid, it is in the state of pn- trefactive fermentation; that the several ingredients in pus are pro- ducts of secretion; that the varieties of purulent matter depend on the proportion of its essential ingredients; that the saline ingredients before named are dissolved in the serous fluid, and that the quantity of these is less than in an equal quantity of expectorated matter, but more than in an equal quantity of serum of blood.
That besides the consistence of pus depending upon the proportion of its essential ingredients, some difference may also arise from the mode or state of coagulation of the matter which gives the opacity.
According to the above inferences, the author conceives that a distinct and definite notion of the substance to be considered as pus is exhibited, and that it will now be readily ascertained what is and what is not pus, by a few easy experiments.
But since it is frequently disguised by the admixture of other matters, and a degree of ambiguity arises, especially in pulmonic diseases, he concludes by endeavouring to elucidate the subject, by remarks on puriform matters expectorated in different cases of pulmonary disorders.
