ATMOSPHERE IN RELATION TO HUMAN LIFE AND HEALTH. 243 



The clothes of scholars should be clean and washable, and there 

 should be no crowding together in the class rooms. 



SEWER AIR. 



Sewer air in sewers of good construction, in good order, and at ordi- 

 nary temperatures, contains very few living organisms discoverable by 

 the usual methods. Microbes are not easily given oft' from sewage 

 unless it be in a state of fermentation, and those which escape soon 

 attach themselves to the wet surfaces of the sewer and drains. Yet 

 there may be microorganisms which are not capable of cultivation 

 and observation by means hitherto tried, but which are the agents 

 concerned in the putrefactive and disease-causing changes set up in 

 organic substances exposed to sewer air. 



Moreover, the presence of a very few pathogenic microbes may be 

 sufficient, when inhaled with the noxious gases in which they float, to 

 set up typhoid and other dangerous disorders. 



It is well to guard against the assumption that negative evidence 

 proves auything in these cases. The bacilli or organisms of smallpox, 

 measles, whooping cough, malaria, etc., are either undiscovered or very 

 difficult to see and to identify. Drinking water which may be clear, 

 bright, and pronounced by microscopic analysis to be pure and excel- 

 lent, may poison by the invisible germs of typhoid which it contains. 

 Analysis of water aud of air is sometimes a less trustworthy arbiter 

 than the senses, or than knowledge of suspicious circumstances. 



Often a family lives in a badly drained house for a long time without 

 suffering anything worse than headaches, diarrhea, sore throat, or loss 

 of appetite. These ailments may be due either to habitual inhalation 

 of the poisonous gases, or to the gases joined with slightly virulent 

 microbes. Depressed vitality gives a strong presumption, if other 

 conditions are wholesome, that drain air enters the house. 



When drains and sewers are out of order, or fermentation is going 

 on, or where there is old sediment, it is probable that a large number 

 of microbes of a disease-producing kind are evolved and carried by the 

 gases and air into houses. The process of decomposition and fermen- 

 tation sets free small bubbles of gas in the liquid and on the wet surface, 

 and these bubbles in bursting scatter a number of small particles into 

 the air. The force with which liquid particles are scattered upward 

 may be observed in the breaking of minute bubbles such as those 

 which rise to the surface of a glass of effervescing water. Experi- 

 ments on various drying and putrefying liquids could hardly fail to 

 furnish interesting results. There seems to be great probability that 

 bacteria or their spores are thrown in quantities into the air from 

 viscous putrefying or fermenting liquids. Certainly a fermenting 

 brewer's vat scatters multitudes of yeast germs into the air, and the 

 case seems strictly comparable. 



