OP ACCIDENTAL HUMOURS. 521 



Pus does not always present precisely the same physical 

 qualities and the same chemical properties. It can be distin- 

 guished mto creamy pus, homogeneous, commonly called most 

 laudable; into serous pus, sanious, or purulent serosity, into 

 glareous pus or puriform mucus; into curdled or clotted pus; 

 into concrete or plastic pus. Besides, pus may be mixed with 

 blood, serosity, excrementitious matters, putrid matter, acci- 

 dental tissues, calculi, virulent matter,- &c. 



In all these cases it is composed, according to Pearson, of a 

 white, opaque, and slightly soluble animal oxide, of a limpid 

 fluid, analogous to the serum of the blood, which holds the 

 animal oxide in suspension, but not in a state of solution; and 

 of an innumerable quantity of microscopic globules. The dif- 

 ferences which it presents depend on the different proportions 

 in which these essential materials are found, as well as the 

 substances which may be found there accidentally. 



821. Pus may be formed in the greater part of the organs. 



The tissue in which suppuration is most frequent and seems 

 the most easy, is the mucous membrane. Some hours after 

 the application of an irritating cause, the physical and chemi- 

 cal properties of mucus are seen to change insensibly into those 

 of pus. When the irritation diminishes and ceases, the pro- 

 perties- of pus are seen to change inversely into mucus. The 

 suppuration of the mucous membrane is accompanied with a 

 slight degree of redness and swelling, and very rarely with 

 ulceration. 



The skin suppurates easily whenever it is irritated and the 

 epidermis removed. This may continue indefinitely, if the 

 irritation is continued, or frequently renewed; the skin then 

 takes on the aspect of an inflamed mucous membrane. 



The cellular tissue being exposed by the removal of the 

 skin, the hemorrhage stops; then flows serosity, which by de- 

 grees takes the character of pus. At the same time the wound- 

 ed surface covers itself with a layer of organizable matter, 

 which becomes vascular and covered with granulations. 



The cellular tissue being irritated by a foreign body or by 

 an unknown cause (spina helmontii) inflames; pus forms in 

 the centre of the phlegmon : this pus is enclosed in a mem- 



