INCUBATION 
tory, that carbon dioxide in the quantities involved, has no 
perceptible effect upon egg shells, it is with some apology that 
I mention that quite a deal of good brains has been spent upon 
the subject by two experiment stations. The data accumulat- 
ed, of course, fails to prove the theory, but it is interesting 
as further evidence of the needlessness in the old fear of 
insufficient ventilation. 
At the Ontario Station, the average amounts of carbon 
dioxide under a large number of hens was .32 of one per cent., 
or about ten times that of fresh air, or one-sixth of that which 
the man breathed so happily in the respiratory calorimeter. 
With incubators, every conceivable scheme was tried to 
change the amount of carbon dioxide. In some, sour milk 
was placed which, in fermenting, gives off the gas in question. 
Others were supplied with buttermilk, presumably to familiar- 
ize the chickens with this article so they would recognize it 
in the fattening rations. In other machines, lamp fumes were 
run in, and to still others, pure carbon dioxide was supplied. 
The percentage of the gas present varied in the machines 
from .06 to .58 of one per cent. The results, of course, vary 
as any run of hatches would. The detailed discussion of the 
hatches and their relation to the amount of carbon dioxide 
as given in Bulletin 160 of the Ontario Station, would be un- 
fortunately confusing to the novice, but would make amusing 
reading for the old poultryman. Speaking of a comparison of 
two hatches, the writer, on page 53 of the bulletin says, “The 
increase in vitality of chicks from the combination of the 
carbon dioxide and moisture over moisture only, amounting, 
as it does, to 4.5 per cent. of the eggs set, seems directly due 
to the higher carbon dioxide content.” I cannot refrain from 
suggesting that if my reader has two incubators, he might set 
up a Chinese prayer machine in front of one and see if he 
cannot in like manner demonstrate the efficacy of Heavenly 
supplications in the hatching of chickens. 
The practical bearing of the subject of ventilation in the 
small incubatcr is almost wholly one of evaporation. The 
majority of such machines are probably too much ventilated. 
In a large and properly constructed hatchery, such as is dis- 
cussed in the last section of this chapter, the entire composi- 
tion of the air, as well as its movement, is entirely under con- 
trol. Nothing has yet been brought to light that indicates any 
particular attention need be given to the composition of such 
air save in regard to its moisture content, but as the control 
of this factor renders it necessary that the air be in a closed 
circuit, and not open to all out-doors, it will be very easy to 
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