THE BACTERIA (SCHIZOMYCETES) 175 



and so destructive that it has been called " the great white 

 plague." Its universal importance demands that a separate 

 paragraph be given to a brief statement concerning it. It is 

 the most destructive disease that affects the human race, and 

 in the United States it causes about one ninth of all deaths. 

 It costs the United States many hundreds of thousands of 

 dollars annually, and, if a money estimate could be placed 

 upon the many untoward circumstances that accompany and 

 follow tuberculosis, the sum would be appalling. 



The tubercle bacilli may infect almost every part of the 

 human body. Though the lungs are the regions most fre- 

 quently attacked, the bones and joints, the intestines, the 

 throat, skin, and other organs often are the regions of growth 

 of these bacilli. 



The growth of tubercle bacilli in the body is usually very 

 slow, and months or years may pass before conspicuous con- 

 sequences follow infection. Furthermore, the germs may live 

 upon a handkerchief, in the floor of a house, in a public 

 building, in public transportation vehicles, in the dirt of the 

 street, etc., for a very long time, and then grow when they 

 are introduced into the human body. Some of the lower ani- 

 mals (cattle, hogs, poultry, etc.) are subject to tuberculosis, 

 and while there seems to be some doubt whether it is of exactly 

 the same kind as tuberculosis of human beings, the dangers 

 are such that careful disposition should be made of all tuber- 

 culous animals. 



The usual source of infection is through the organs of 

 breathing, though the germs may be carried into the mouth 

 and other organs by means of milk and other food. Since the 

 dried or partially dried tubercle bacilli may be transported by 

 the air, it is evident that the greatest precaution should be 

 taken to keep the air from becoming contaminated with these 

 germs. Furthermore, it is known that when tubercle bacilli 

 are moist, the direct light of the sun has a destructive effect 

 upon them, and that fresh air is likely to contain fewer 

 tubercle bacilli than the " close " air of rooms in which many 



