312 VENTILATION 



340. Effect of Breathing upon the Composition of Air. 



When man, or any animal, breathes this air, oxygen is consumed 

 and carbon dioxide and water vapor are given off. When 

 many people are gathered together in a closed, nearly air-tight 

 room for some time, the air becomes much changec^ We 

 say that the air becomes VITIATED. If some of those present 

 are suffering from colds, pneumonia, tuberculosis, or other 

 communicable diseases, the disease-producing germs (see 

 Chap. VIII) are certain to be present in the air. 



341. Theories Regarding Vitiated Air. For many years the 

 most objectionable factor in vitiated air was supposed to be 

 small amounts of poisonous volatile matter, organic com- 

 pounds, expelled from the lungs with the breath. This sup- 

 position gave rise to the term CROWD POISONING. Some years 

 ago doubt arose as to the correctness of this supposition. 

 Very careful experiments by skillful investigators employed 

 by the government, failed to show the presence of this supposed 

 objectionable matter. Few scientists now believe in the 

 CROWD POISON THEORY of vitiated air. It is now generally 

 believed and taught by teachers of hygiene and sanitary 

 science, that, as far as there is any offensive odor in the breath, 

 it is probably due to decayed teeth, effects of catarrh, decom- 

 position of food in. the mouth, or disordered stomach. 



Moreover, it is now believed that most of the unpleasant 

 odors noticeable when any crowd gathers indoors come from 

 the unclean bodies and clothing of those present. The skin 

 of -even the cleanliest person is constantly giving off waste 

 material. A considerable portion of the waste materials of the 

 body is given off through the pores of the skin. The offensive 

 odors so characteristic of theaters, moving-picture shows, 

 schoolrooms, auditoriums, and churches are now generally be- 

 lieved to be caused chiefly by excretions from the skin, not t 

 from the lungs. In general, the theory of crowd poison has j 

 been abandoned. 



342. Theories Regarding Ventilation. As already stated, 

 pure country air usually contains about 0.03 per cent., or 3 



