INCUBATION 
surprised at our poor results in artificial incubation. Compared 
with our acknowledged records of less than 50 per cent. 
hatches, he quotes the results obtained in hatching 18,000 
eggs at an English experiment station as 62 per cent. I have 
not obtained any data of English humidity, but it is undoubt- 
edly more uniform than the eastern United States. 
Ventilation—Carbon Dioxide. 
The last of the four life requisites we have to consider is 
that of oxygen. The chick in the shell, like a fish, breathes 
oxygen which is dissolved in a liquid. A special breathing 
organ is developed for the chick during its embryonic stages 
and floats in the white and absorbs the oxygen and gives off 
carbon dioxide. The amount of this breathing that occurs 
in the chick is at first insignificant, but increases with de- 
velopment. At no time, however, is it anywhere equal to that 
of the hatched chicks, for the physiological function to be 
maintained by the unhatched chicks requires little energy and 
little oxidation. 
Upon the subject of ventilation in general, a great mis- 
understanding exists. Be it far from me to say anything that 
will cause either my readers or his chickens to sleep less in 
the fresh air, yet for the love of truth and for the simplifica- 
tion of the problem of incubation, the real tacts about ventila- 
tion must be given. 
In breathing, oxygen is absorbed and carbon dioxide and 
water vapor are given off. It is popularly held that abundance 
of fresh air is necessary to supply the oxygen for breathing 
and that carbon dioxide is a poison. Both are mistakes. The 
amount of oxygen normally in the air is about 20 per cent. 
Of carbon dioxide there is normally three hundredths of one 
per cent. During breathing these gasses are exchanged in 
about equal volume. A doubling or tripling of carbon dioxide 
was formerly thought to be “very dangerous.” Now, if the 
carbon dioxide were increased 100 times, we would have only 
three per cent., and have seventeen per cent. of oxygen 
remaining. This oxygen would still be of sufficient pressure 
to readily pass into the blood. We might breathe a little 
faster to make up for the lessened oxygen pressure. In fact 
such a condition of the air would not be unlike the effects of 
higher altitudes. 
Some investigations recently conducted at the U. S. Experi- 
ment Station for human nutrition, have shown the utter mis- 
conception of the old idea of ventilation. The respiratory cal- 
orimeter is an air-tight compartment in which men are con- 
fined for a week or more at a time while studies are being 
made concerning heat and energy yielded by food products. 
88 
