THE RELATION OF BACTERIA TO DISEASE 51 



solidly around the scene of conflict, forming a dense ring or 

 wall which shuts off the fighters from the rest of the body. 

 Inside the ring many of the combatants are killed, so that, 

 in addition to living bacteria and living leukocytes, there 

 is now an accummulation of cellular and bacterial debris. 

 When the inflammation has proceeded in this way we have 

 an abscess. The pus in an abscess is composed of leuko- 

 cytes, broken-down tissue cells, bacteria, fibrin, serum, 

 and debris. 



However, the inflammation may take a somewhat dif- 

 ferent course an abscess does not always result. The 

 course depends mainly on the nature and virulence of the 

 invading bacterium, the part of the body invaded, and the 

 resistance of the patient. Thus it may happen that the 

 invading organisms are so virulent or so numerous that 

 before the leukocytes and other cells have completed their 

 wall about the scene of conflict the invading bacteria have 

 extended into the tissues far beyond. Again and again the 

 leukocytes and other body cells gather and attempt to 

 localize the conflict, the inflammation meantime involving 

 a large area of tissue. This kind of inflammation is spoken 

 of as a cellulitis or a purulent infiltration; it is often due to 

 the streptococcus. 



In typhoid fever we meet with another type of inflam- 

 mation, namely, an ulceration. In this disease we have a 

 localization of typhoid bacilli in certain lymph-follicles 

 known as "Peyer's patches," situated in the wall of the 

 small intestine. Instead of forming circumscribed ab- 

 scesses, the inflammation here produces ulcers opening on 

 the inner surface of the gut. In other words, an ulcer is 

 an abscess whose outer wall is missing. 



When bacteria invade the pleura a variety of inflam- 



