28 POPULAR SCIENCE MONTHLY 



wholesome effects. Special provision must be made for drying the air 

 to keep down the relative humidity in the rooms so cooled. In moist 

 and warm weather it would otherwise reach the saturation point. Such 

 a condition is not only uncomfortable, but can become very unhealthy. 

 The science of artificial cooling is as yet very little understood by 

 the average layman and any devices which do not give perfect control 

 over humidity must be cautioned against. 



Ventilating apparatus itself may become a source of contamination 

 if improperly designed, operated or maintained. Air filters have been 

 found, for instance, which were intended to arrest the dust, but actually 

 also arrest nearly all the fresh air. Some of these filters can not be 

 cleaned or renewed without spilling the very impurities collected into 

 the air ducts and thence into the rooms. Mechanical ventilating de- 

 vices too often defeat their usefulness by lack of control over air cur- 

 rents and temperature, which either puts them out of service, or the 

 persons for whose benefit they were intended. 



Vitiation through Animal Life. — The last, but not the least, among 

 the sources of vitiation is the presence of animal life or of man. 

 Theoretically, perhaps, this may be called the only unavoidable factor, 

 or the one which must be met by ventilation. The exhalation of car- 

 bonic acid in place of the oxygen inhaled reduces the life-giving quality 

 of the air, or its power of regenerating the blood. Exhaled air, more- 

 over, is charged with vapor and organic matter. The substance, called 

 effluvia, which emanates from the surface of the human body is also 

 of organic nature. It is harmless enough when permitted to dry and 

 disperse, but in the moist and warm air of over-crowded rooms it 

 quickly putrefies and becomes obnoxious. It can be recognized by that 

 pungent odor characteristic of a sweltering mass of people. Whatever 

 ill effects may be due to effluvia come through the action of odor on 

 the nerves, rather than through inhaling this comparatively innocuous 

 matter. The excess of heat and moisture produced by an audience as 

 previously mentioned is now regarded as more than a temporary dis- 

 comfort, quite aside from the danger in subsequent exposure to cold. 

 Exhaled air, effluvia and heat thus combine, in varying proportions, to 

 make room air unfit for breathing. In crowded meeting places they 

 are the principal sources of vitiation, which may practically determine 

 the artificial supply of air, while, for instance, in dwellings, offices and 

 shops with liberal space allowance and plenty of exposure they are 

 often a negligible quantity compared with the sources of contamination. 



Suggestions for Relief 

 The remedy for the unhealthy conditions described naturally lies 

 in systematic sanitation of the air; indoors as well as out-of-doors. 

 The methods of carrying on such work are indicated by the causes 



