No. 550] 



BREEDING MICE 



603 



which is added "gold-dust" and a small amount of petro- 

 leum ; the nest-boxes, into which the mice are put at the 

 time of cleaning, are partly closed and then removed from 

 the case. 



Essential to intensive breeding is an adequately 

 equipped case. A most essential requisite is a wire mesh 

 bottom through which waste material readily falls. If 

 such a case be placed on a table with a trough-top lined 

 with galvanized iron, waste matter can easily be drained 

 into a sink. For nests the case is provided with three- 

 fourth sized chalk boxes filled two-thirds full of shredded 

 paper. Food (wheat) is procured by the mice through 

 an opening in the front of the nest box from bird cups 

 placed inside of the box. These are filled from the out- 

 side without opening the case. Water may be kept in 

 excellent condition in test-tubes which are closed suffi- 

 ciently to retain the water drop when the tube is inverted 

 in the case ; these are filled from a siphon bottle. 



A knowledge of breeding habits is of great importance 

 m intensive breeeding. Copulation in mice is a well- 

 defined act, which lasts from ten to twenty-five seconds 

 and is followed by a more or less complete rest. It nor- 

 mally takes place on the day that a litter is born. In 

 females that have gone through a period of rest it will 

 usually occur a few days after the female has been put 

 with the male. Copulation may or may not result in fer- 

 tility. By a selection of males and females with a high 

 index of fertility the number of offspring may be greatly 

 increased. 



The period which a non-suckling mother carries her 

 young is a few hours short of twenty days. A mother 

 suckling young, on the other hand, carries her litter 

 twenty plus the number that she is suckling. Thus a 

 mother suckling five will go practically (20+5) twenty- 

 five days, while one suckling ten may be expected to run 

 (20+10) thirty days. 



In rearing the young it is well to remember that the 

 neatest mortality results within the first two or three 

 d ays of life. At this time the young must be kept warm. 

 Under bad conditions the mother may destroy them. 



