RELATION OF BACTERIA TO DISEASE. 89 
poisons in foods, ete., 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. 
