PART IV. 



PATHOGENIC BACTERIA. 



Suppuration and Allied Conditions. — ^The occurrence of 

 suppuration is characterized by certain appearances which we 

 are accustomed to describe under the name of inflammation. 

 The study of inflammation belongs to pathology, and cannot 

 be considered fully here. However, certain evidences which 

 are characteristic of the suppurative variety of inflammation 

 need to be outlined on account of their relation to the action 

 of the pyogenic bacteria. 



In a suppurating area, as is well known, the blood-vessels 

 are dilated, and the lymph-spaces become filled with serum. 

 Leukocytes are attracted to the neighborhood in large num- 

 bers, by positive chemotaxis, and crowd the small veins and 

 capillaries. The leukocytes, by reason of their ameboid move- 

 ment, pass through the walls of the vessels at little openings 

 filled with cement-substance, situated between the lining endo- 

 thelial cells. According to the theory of phagocytosis, they are 

 bent on finding the irritant which has led to the inflammation, 

 and upon attacking it and rendering it harmless. At the 

 point which appears to be the center of the inflammatory area 

 there is usually, but not always, a necrosis of the cells of the 

 tissue; this constitutes the central slough or the famihar core 

 found in some boils. The necrosis is to be attributed to poi- 

 sons formed by the micrococci. In sections cut through such 

 an abscess the nuclei of the necrotic cells in the center fail 

 to take the nuclear stain; the necrotic mass does not stain, 

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