INCUBATION 
It being inconvenient to analyze such an immense volume of 
air as would be necessary to keep the room freshened accord- 
ing to conventional ventilation standards, experiments 
were made to see how vitiated the air could be made without 
causing ill effects to the subject. 
This led to a remarkable series of experiments in which it 
was repeatedly demonstrated that a man could live and work 
for a week at a time without experiencing any ill effects 
whatever in an atmosphere of his own breath containing as 
high as 1.86 per cent. of carbon dioxide, or, in other words, 
the air had its impurity increased 62 times. This agrees with 
what every chemist and physiologist has long known, and that 
is that carbon dioxide is not poisonous, but is a harmless 
dilutent just as nitrogen. This does not mean that a man or 
animal may not die of suffocation, but that these are smother- 
ed, as they are drowned, by a real absence of oxygen, not 
poisoned by a fraction of 1 per cent. of carbon dioxide. 
In the same series of experiments, search was made for the 
mysterious poisons of the breath which many who had learned 
of the actual harmlessness of carbon dioxide alleged to be the 
cause of the ill effects attributed to foul air. Without discus- 
sion, I will say that the investigators failed to find such 
poisons, but concluded that the sense of suffocation in an un- 
ventilated room is due not to carbon dioxide or other “poison- 
ous” respiratory products, but is wholly due to warmth, water 
vapor, and the unpleasant odors given off by the body. 
The subject of ventilation has always been a bone of con- 
tention in incubator discussions. With its little understood 
real importance, as shown in the previous section, and the 
greatly exaggerated popular notions of the importance of 
oxygen and imagined poisonous qualities of carbon dioxide, 
the confusion in the subject should cause little wonder. 
A few years ago some one with an investigating mind de- 
cided to see if incubators were properly ventilated, and pro- 
ceeded to make carbon dioxide determinations of the air under 
a hen and in an incubator. The air under the hen was found 
to contain the most of the obnoxious gas. Now, this informa- 
tion was disconcerting, for the hen had always been consider- 
ed the source of all incubator wisdow. Clearly the perfection 
of the hen or the conception of pure air must be sacrificed. 
Chemistry here came to the rescue, and said that carbon di- 
oxide mixed with water, formed an acid and acid would dis- 
solve the lime of an egg shell. Evidently the hen was sacri- 
ficing her own health by breathing impure air in order to 
soften up the shells a little so the chicks could get out. Since 
it could have been demonstrated in a few hours in any labora- 
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