FACTORY SANITATION WINSLOW. 613 



sion, headache, dizziness, and the other symptoms associated with 

 badly ventilated rooms begin to manifest themselves. At 78° with 

 saturated air Haldane found that the temperature of the body itself 

 began to rise. The wonderful heat-regulating mechanism which 

 enables us to adjust ourselves to our environment had broken down 

 and an actual state of fever had set in. Overheating and excess of 

 moisture is the very worst condition existing in the atmosphere and 

 the very commonest. 



The importance of the chemical impurities in the air has dwindled 

 rapidly with the investigations of recent years. The common index 

 of vitiation, due either to human beings or to lighting and heating 

 appliances, is carbon dioxide; but carbon dioxide in itself has no 

 harmful effects in tenfold the concentration it ever reaches in ordi- 

 nary factory air. Nor is there any reduction of oxygen which 

 has any physiological significance. In the Black Hole of Calcutta 

 and below the battened-down hatches of the ship Londonderry there 

 was actual suffocation due to oxygen starvation, but this can never 

 occur under normal conditions of habitation. It was long believed 

 that the carbon dioxide was an index of some subtle and mysterious 

 "crowd poison" or "morbific matter." All attempts to prove the 

 existence of such poisons have incontinently failed. There are very 

 perceptible odors in an ill-ventilated room, due to decomposing 

 organic matter on the bodies, in the mouths, and on the clothes of the 

 occupants. These odors may exert an unfavorable psychical effect 

 upon the sensitively organized, but as a rule they are not noticed by 

 those in the room, but only by those who enter it from a fresher atmos- 

 phere. Careful laboratory experiments have quite failed to demon- 

 strate any unfavorable effects from rebreathed air if the surrounding 

 temperature is kept at a proper level. In exhaustive experiments by 

 Benedict and Milner (Bulletin 136, Office of Experiment Stations, 

 U. S. Department of Agriculture), 17 different subjects were kept for 

 periods varying from 2 hours to 13 days in a small chamber with a 

 capacity of 189 cubic feet in which the air was changed only slowly 

 while the temperature was kept down from outside. The amount 

 of carbon dioxide was usually over 35 parts (or eight to nine times 

 the normal), and during the clay when the subject was active it was 

 over 100 parts, and at one time it reached 240 parts. Yet there was 

 no perceptible injurious effect. 



The main point in air conditioning is, then, the maintenance of a 

 low temperature and of a humidity not too excessive. For maximum 

 efficiency the temperature should never pass 70° F., and the humidity 

 should not be above 70 per cent of saturation. At the same time a 

 too low humidity should also be avoided. We have little exact infor- 

 mation upon this point, but it is a matter of common knowledge with 

 many persons that very dry air, especially at 70° or over, is excessively 

 stimulating and produces nervousness and discomfort. It would 



