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In breeding mice, one should be sure to use strong, healthy animals. If the mice are obtained from an unknown stock, they should be isolated for two weeks, and if any of them become sick during this time they must be discarded. Unless this precaution is taken, an epidemic will devastate one's own stock.
At the time of mating, the female mice should be from 8 to 10 weeks old, and should weigh from 17 to 18 gm. The males should be from 8 to 10 weeks old, and should weigh at least 20 gm. The period of gestation of the mouse is about twenty-one days. The average litter is five, although some females give birth to as many as twelve. It is best not to put more than four females with one male. The males should not be used more than three or four months, while the females should