256 PATHOLOGY Of 1 THE BLOOD AND CIRCULATION. 



tion there are vascular and tissue changes ; but there is a 

 great variability in the character of inflammations resulting 

 from differences in the nature of the irritants, their persist- 

 ence, and in the tissues on which they act. 



Irritants may be divided into organized and unorganized, 

 the former including animal and vegetable parasites, and the 

 latter mechanical, physical, and chemical influences. The 

 migrating leukocytes play the more important part when the 

 irritant is organized. There is a very considerable difference 

 between a blister in which there is an enormous serous exu- 

 date containing but few leukocytes, and the slight serous but 

 enormous cellular exudate produced by pyogenic cocci. 



Though this property of inducing the migration of a large 

 number of leukocytes is well recognized as belonging to cer- 

 tain micro-organisms, yet the various other factors concerned 

 in bringing about such a result are not fully understood. In- 

 tense cold produces an inflammation which is accompanied by 

 an excessive migration of leukocytes, while the inflammation 

 produced by heat is accompanied by the emigration of but 

 very few leukocytes. 



Purulent or suppurative inflammation is a variety character- 

 ized by an excessive migration of polymorphonuclear leuko- 

 cytes or neutrophiles, and a tendency to liquefaction of affected 

 areas i. e. 9 by the formation of pus. 



Pus is a creamy fluid, of specific gravity about 1030, and 

 usually alkaline in reaction. If it be allowed to stand, it 

 separates into two layers. The upper the liquor puris is 

 a clear fluid, yellowish in tint, and resembling blood-serum. 

 If a drop from the opaque lower layer be examined under 

 the microscope, one will find suspended therein a great num- 

 ber of colorless, granular, round cells (see Fig. 98). Their 

 peculiar horseshoe-shaped nuclei identify them as polymor- 

 phonuclear leukocytes. If the specimen is from an acute 

 abscess, in a large number of the cells amo?boid movements 

 may be noted, especially if examined on a warm stage. 



A circumscribed collection of pus in any tissue is known 

 as an abscess. In addition to the excessive migration of 

 leukocytes which characterizes purulent inflammation, there 

 are also a necrosis and liquefaction of the tissue at a given 

 point, setting free, as it were, the migrated cells within this 



