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 bod y 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 day 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 
