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 

 the woods and fields there is a "poison dogwood ;" or 



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- 



Communicabie 

 Diseases 



