INCUBATION 
forced with straw. The walls are two or three feet thick. 
Inside, the main rooms are little clay domes with two floors. 
The hatching season begins the middle of January and lasts 
three months. A couple of weeks before the hatching begins, 
the fireproof house is filled with straw which is set afire, thor- 
oughly warming the hatchery. The ashes are then taken out 
and little fires built in pots are set around the outside of the 
big room. The little clay rooms with the double floors are 
now filled with eggs. That is, one is filled at a time, the idea 
being to have fresh eggs entering and chicks moving out in 
a regular order, so as not to cause radical changes in the 
temperature of the hatchery. 
No thermometer is used, but the operator has a very highly 
cultivated sense of temperature, such as is possessed by a 
cheese maker or dynamite dryer. About the twelfth day the 
eggs are moved to the upper part of the little interior rooms 
where they are further removed from the heated floor. The 
eggs are turned and tested out much as in this country. They 
are never cooled and the room is full of the fumes and smoke 
of burning straw. The ventilation provided is incidental. 
This is about the whole story save for results. The incuba- 
tor men pay back three chicks for four eggs, and take their 
profits by selling the extra chicks that are hatched above the 
75 per cent. This statement is in itself so astonishing and 
yet convincing, that to add that the hatch runs between 85 per 
cent. and 90 per cent. of all eggs set, and that the incubators 
of the Nile Delta hatch about 75,000,000 chicks a year seems 
almost superfluous. As for the explanation of the results of the 
Hgyptian incubators compared with the American kerosene 
lamp type, I think it can best be brought about by a considera- 
tion in detail of the scientific principles of incubators. 
Principles of Jncubation. 
HEAT.—To keep animal life, once started, alive and grow- 
ing, we need: First, a suitable surrounding temperature. 
Second, a fairly constant proportion of water in the body sub- 
stance. Third, oxygen. Fourth, food. 
Now, a fertile egg is a living young animal and as such its 
wants should be considered. We may at once dispose of the 
food problem of the unhatched chick, by saying that the food 
is the contents of the egg at the time of laying, and as far as 
incubation is concerned, is beyond our control. 
In consideration of external temperature in its relation to 
life, we should note: (A) the optimum temperature; (B) the 
range of temperature consistent with general good health; 
(C) the range at which death occurs. Just to show the prin- 
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