CHARACTERS OF PUS. 189 



any higher organization. Pus is totally aplastic, and its corpuscles 

 possess a very low vitality. 



Origin and Characteristics of Pus. 



Thus pus is not a secretion, but is a changed exudation; the change 

 being due to various causes, among which the action of the atmo- 

 sphere is one of the most prominent. In granulating wounds, there- 

 fore, we find a pure exudation constantly appearing on the surface 

 of the living tissues, with exudation-corpuscles and cells forming in 

 it ; while the external portion of the exudation has become true pus. 

 All the intervening grades of development between these two ex- 

 tremes will, of course, present themselves. Flakes or fibrillae of 

 coagulated fibrine will also be often found mixed with the pus first 

 formed in an abscess ; these having been formed by simple fibril- 

 lation as the initiatory step, and before the pus-corpuscles are 

 developed. It is also certain that pus may be formed from a solid 

 mass of fibrine after its coagulation. (Vogel.) 



Thus, also, it appears that pus is formed from an exudation by a 

 "retrogressive metamorphosis." (Wedl.) 



Characters of Pus. 



Pus, when perfectly formed genuine pus is a yellowish, creamy, 

 thick fluid, of a specific gravity of 1030 to 1033 (Oluge). and a feeble 

 alkaline reaction. Exposed to the air, however, it soon undergoes 

 transformations ; passing into the acid fermentation, or the alkaline, 

 or into putrefaction. In cases of phthisis, pus is sometimes acid 

 when expectorated. 



The whole amount of solid constituents in- pus is 140 to 160 parts 

 in 1,000, of which only 5 to 6 per cent, consists of mineral sub- 

 stances. Of the last, the soluble salts predominate, being propor- 

 tioned to the insoluble as 7 or even 9 to 1. It also contains the 

 oxide of iron. 



Seen under the microscope, pus consists of (1) a fluid portion, 

 containing (2) histological elements the pus (cytoid) corpuscles. 

 An analysis of pus, as compared with that of the blood, shows the 

 former to contain far less albumen, no fibrine at all, far more fat, 

 and about three times as much chloride of sodium, the latter being 

 confined almost exclusively to the pus-serum.' Fibrine, whether 

 coagulated or not, is sometimes found mixed with pus, however ; a 

 portion of the exudation still remaining unchanged. " Connective 

 tissue-cells" (nucleated fibres), may also be found in pus, from a 

 higher organization of a part of the exudation. (Fig. 104.) 



1. The fluid portion (pus serum, or liquor puris) is perfectly clear, 

 colorless or slightly yellowish, has a feeble alkaline reaction, and 

 coagulates, on being heated, into a dense white mass. Its main con- 

 stituent is albumen, which constitutes from 12 to 37 parts in 1,000. 

 Some of the fat in pus also belongs to the serum, and about 1 per 

 cent, of cholesterine. 



