190 THE HYGIENE OF RESPIRATION 



<of cases for the spread of disease. In this way, we are 

 exposed to hordes of disease germs, which are con- 

 stantly lodging in the mucous membranes of nose, throat 

 and lungs. If we are fortunate, they are thrown out by 

 the cilia or destroyed by the white blood corpuscles. If 

 not, such diseases as colds, consumption, pneumonia and 

 diphtheria result. The problem of diminishing the 

 amount of dust in cities is therefore exceedingly 

 important. 



Coughing. In addition to the dried particles of 

 microbe-laden sputum and other excretions, air also 

 contains at times particles of moisture which are pro- 

 jected into it by those who cough. These particles are 

 so fine that they quickly dry and float about for some 

 time before settling. Careful examinations have shown 

 that they carry such disease germs as exist in the mucus 

 covering the air passages of the lungs, the bronchi and 

 trachea, the pharynx, nose and throat of those who are 

 coughing or sneezing. Many diseases are directly trans- 

 mitted in this way from diseased to well persons. Thor- 

 ough ventilation and covering the mouth when cough- 

 ing reduce the danger of their transmission very mate- 

 rially, although they do not remove it entirely. Only by 

 the isolation of those diseased, can the danger be 

 eliminated. 



Sewer gas. Sewer air, which is disagreeable chiefly 

 because of its odor, is not necessarily poisonous, although 

 it may contain poisonous gases such as coal gas and 

 illuminating gas. As we have seen, both coal gas and 

 illuminating gas contain the deadly carbon monoxide 

 (CO) , which has been generated by burning carbon at too 

 low a temperature for complete oxidation. 



Care of nose. In addition to providing the organs of 

 respiration with as pure air as possible for breathing, 



