apparatus for the maintenance of controlled conditions in which eggs can be hatched artificially. Incubator houses with double walls of mud, a fireroom, and several compartments each holding about 6,000 hens' eggs were developed in ancient times; the Chinese have long used baskets with a capacity of about 5,000 eggs that are alternated with layers of heated wheat. In the United States small incubators were developed in the 1840s and large ones have been used since 1910; some commercial models have trays for as many as one million eggs. The modern apparatus, with computer-controlled temperature and humidity and devices for turning the eggs, is widely used in commercial chick production. Eggs are selected for size, weight, and shell texture and often are candled after a week in the incubator in order to remove infertile eggs. The small-scale apparatus for hatching eggs inspired the invention of incubators for prematurely born human infants, whose lives are often saved in an environment of controlled heat, humidity, and ventilation. Another type of incubator has been developed for the culture of microorganisms.

See R. E. Austic and M. C. Nesheim, Poultry Production (13th ed. 1990); M. North, Commercial Chicken Production (1990).

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