884 



and a sulphate, beside traces of phosphate of magnesia, oxide of iron, 

 and verifiable matter (probably silica). 



The different kinds of pus are next mixed with large quantities 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 subse- 

 quent 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 coagulable 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 pu- 

 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 mat- 

 ters, and a degree of ambiguity arises, especially in pulmonic dis- 

 eases, he concludes by endeavouring to elucidate the subject, by re- 

 marks on puriform matters expectorated in different cases of pul- 

 monary disorders. 



