490 
THE BIOLOGY OF DISEASE 
day. For this reason great care should be taken in destroy¬ 
ing the sputum of patients, for if the germs become dry, 
they are carried about as dust particles. 
Tuberculosis and other disease germs are so numerous 
that it is impossible to escape taking some of them into our 
bodies, but they usually do us no harm unless we are in a 
weakened condition. 
Modern methods of cleaning the streets by flushing with 
water, keeping garbage covered, and wiping up the dust 
Figure 424. — Tuberculosis Cure, Summer. 
in our homes instead of using the old-fashioned feather 
duster are doing much to keep down the number of germs 
in the air which we breathe. 
The bacteria that are breathed in from the air may find 
some weak place in the lungs in which to take up their 
parasitic lives. Those which enter on the food pass from 
the digestive tract into the blood and are eventually carried 
to the lungs. The introduction of tuberculosis germs in 
