RELATION OF BACTERIA TO DISEASE. gg 



poisons in foods, etc., which are absorbable, and which 

 when taken with food or drink can produce a chemical 

 intoxication. That they are really deleterious is shown 

 by the fact that if a sufficient quantity of their pure 

 cultures is injected into the tissues suppuration and ab- 

 scesses are produced by the toxic substances contained 

 within them. 



Closely allied to the bacteria which cannot grow at 

 all in the bodies of warm-blooded animals are those 

 which are able to grow in or upon certain circum- 

 scribed areas only. Thus the diphtheria bacilli grow 

 upon the abraded mucous membranes of the respiratory 

 tract, but cannot develop in the blood or in the subcu- 

 taneous tissues. The cholera spirilla develop in the in- 

 flamed intestinal mucous membrane, but cannot grow 

 in the respiratory tract, blood, or tissues. The tetanus 

 bacilli develop in wounds of the subcutaneous tissues, 

 but cannot grow on the body-surface or in the blood. 



Another group of bacteria find, indeed, certain regions 

 most suitable in their conditions for growth, but under 

 circumstances favorable for them are capable of more ex- 

 tensive growth. Thus the typhoid bacillus grows most 

 luxuriantly in the Peyer's patches and mesenteric glands, 

 but also invades the blood, spleen, and other regions. 

 The tubercle bacillus often remains localized in the 

 apex of a lung or a gland for years, but at any time 

 may invade many tissues of the body. The gonococcus 

 finds the mucous membrane of the genito-urinary tract 

 most suitable for its development, but also frequently is 

 capable of growth in the peritoneum and even some- 

 times in the general circulation. The pneumococcus 

 develops most readily in the lungs, but also invades the 

 connective tissues, serous membranes, and the blood. 



