DISEASE GERMS 
We have seen that these dust-plants may spoil our 
property and thereby cause us much expense. Did 
they do nothing else, we might not spend so much time 
or labor in studying them and their work. 
Just as among the hundreds of beautiful flowers in 
poison dogwoodor 
i 
n 
i 
b 
a 
FIG. 40. THE BACILLUS OF TUBERCULOSIS. 
(a) Taken from lung tissue, (b) As sometimes found in the sputum. 
among the luscious mushrooms a deadly “Amanita 
or as in a great city among the thousands of honest, 
harmless, law-abiding citizens there is an occasional 
thief or murderer; so among the millions of helpful 
bacteria there are a few which in man and animals 
cause disease of greater or less virulence. 
These are called infectious or contagious diseases. 
They are carried either by actual contact with dis- 
the woods and fields there is a 
Communicable 
Diseases 
75 
