CARBON DIOXIDE UNDER SITTING HENS 159 
at the same time agree very closely with results given here, 
showing that the figures for carbon dioxide are not much be- 
low the actual amount, which one might believe to be true 
if there was a large admixture of outside air with the small 
amount found under the hen. 
This rapid method of drawing the air shows what a later 
method does not show so well, and that is, the uniform in- 
crease of carbon dioxide during the incubation period where a 
slower process was employed, as in Table II, where the hen 
would raise herself from the eggs or move about, thus seri- 
ously interfering with the taking of like samples because the 
conditions would be different each day. Samples of air were 
drawn from a hen setting on china eggs and from the air of 
the room. , 
Although there was a slightly higher amount under the 
hen than in the room no agreement could be found with the 
work of the. Utah Station where as much CO2 was 
found under the hen with china eggs as with good eggs.* Ina 
jarge number of cases where china eggs were used or the 
chicks died in the shell as in another experiment carried on at 
this time, it was found that the air under the hen contained 
very little more carbon dioxide than the air of the room. No 
experiment was made to find the source of this increase. A 
little doubtless comes from the hen’s body and some would 
come from respired air caught and held in the feathers of the 
hen as she pecked herself or adjusted the eggs. 
Table I shows conclusively, as does Table II, that when a 
hen is setting on good eggs, the CO2 can be accounted for by 
the CO2 given off by the growing chick within the egg. Al- 
though variable, the amount of carbon dioxide in 10,000 pts. 
of air by weight does not exceed 6.7 pts. after the 13th under 
Hen A with china eggs, while under Hen B there is a gradual 
increase from 3.8 to 22 pts. and a corresponding increase in 
the case of Hen C. 
The Pettenk6fer titration method was used to obtain results 
given in Table II. Samples were taken by filling 500 c.c. 
flasks with distilled water and allowing it to drip out slowly, 
* Note Bulletin 102. 
