Suppurative Iiiflaiinnation. 



281 



emigrated leucocytes, constitutes the tluid catarrhal secretion. On 

 serous surfaces exudation is also attended with desquamation of 

 the endothelial cells, antl the exudate accumulates in the cavity 

 lined -by the serous membrane. A collection of pus in one of the 

 larg-e structural cavities of the body (pleura, joint, antrum of High- 

 more) is called an empyema {^n-wveiv, to contain pus). When pus 

 is distributed all through the spaces and meshes of tissue, it gives 

 the latter a dull yellowish-white or gray color and can be expressed 

 irom it in drops by squeezing between the fingers (purulent infil- 



a — 





Fig. u8. 



riuulent nephritis of mixed type, from calf: «. microscopic abscess: h. eml)oliis : c. 

 normal urinary tubules : d. urinary tubules devoid of their epithelium, con- 

 taining coagulated material. 



tration). Where it collects in larger lymph spaces or occurs in cav- 

 ities formed by local liquefaction of the tissue, it constitutes an 

 abscess (pus sac), that is, a hollow space filled with pus; from pro- 

 gressive tissue destruction and continued entrance of leucocytes 

 such an abscess may attain considerable dimensions (size of a fist 

 or head). A circumscribed collection of pus in the stratum Mal- 

 pighii. elevating the keratous epiderm over it. constitutes a 

 pustule (pus vesicle). When a ])urulent infiltration extends over a 

 large area of subcutaneous, subiiuicous or other loose cellular tis- 



