BACTERIA AND DISEASE 391 



is slow. It usually lasts for years rather than months or weeks. It 

 produces but little pain, and those who suffer with it are usually hopeful 

 of recovery. They may be expected to recover if they take the trouble 

 to follow the proper mode of life. 



695. Tendency to consumption. Tubercle bacteria are 

 very often present in the dust that fills the air in streets 

 and houses. A closed room acts like a trap for dust, and 

 the air in it will have more germs per cubic foot than the 

 air outside. If a person is vigorous and well nourished, 

 and always has fresh air to breathe, his body is not a favor- 

 able soil for the growth of tubercle bacteria; but if his 

 muscles are poorly developed and his breathing is restricted 

 from any cause whatever, or if he sleeps in a poorly ven- 

 tilated room, he is very liable to take the disease. When 

 the breathing is deep and forcible, the bacteria are kept in 

 constant motion and have little chance to lodge and grow. 

 Deep breathing of fresh air also promotes a good circula- 

 tion, and healthy blood has great power to destroy the few 

 germs that may find lodgment. On the other hand, if the 

 air in any part of the lungs is not changed thoroughly and 

 often, bacteria may remain in the air sacs and smaller 

 bronchi, and multiply there ; and if foul air is breathed over 

 and over, the blood is not able to destroy the germs. 



Thus it happens that such persons as clerks and students, 

 who sit still a large part of the time and breathe lightly, are 

 much more likely to take consumption than those who, like 

 explorers, hunters, pioneer miners, and many farmers, lead 

 a life of muscular activity in the open air, though they are 

 constantly exposed to inclement weather. And thus it is 

 that men who live and labor all day in pure air often con- 

 tract consumption from close sleeping rooms when their 

 mode of life otherwise would insure their freedom from 

 almost all forms of infection. 



