CAUSING CHRONIC INFECTIONS. 
97 
sions and ascitic fluid the number of tubercle bacilli is 
always small; so to detect them the inoculation of 
guinea-pigs with the fluid is often practised. If 
tubercle bacilli are present in the fluid injected, the 
disease develops in the animal after a period of three 
to six weeks. In tuberculous meningitis the spinal 
fluid is often clear and the tubercle bacilli difficult to 
find. If, however, the fluid is allowed to stand ten to 
twelve hours a film or clot forms in which the tubercle 
bacilli can be found. The tubercle bacillus may cause 
infection by entering the body in the following ways:— 
Hereditary transmission, long believed to be a 
common occurrence, has not been proven among human 
beings. In very rare instances the bacilli may pass 
from the mother to the child in the uterus, but this de¬ 
pends upon some injury or disease of the placenta. 
Respiratory: This is the most common way that 
infection takes place. The sputum of consumptives is 
the direct carrier of the infection. Deposited in houses, 
on floors and streets, the bacilli become incorporated 
with the dust which is breathed in by those in close 
contact with the patients. 
Intestinal: This is more common in children than 
in adults. The bacilli gain entrance through the milk 
from tuberculous cattle or food infected by consump¬ 
tive people. The habit children have of putting every¬ 
thing into their mouths is responsible for many infec¬ 
tions, particularly in houses where consumptives are 
living. The bacilli resist the action of the acid in the 
stomach, and in the intestine may penetrate the 
7 
Exudates 
Path of 
infection 
