54 LABORATORY MOUSE 



Water. Water standing in an open dish in a mouse cage 

 becomes quickly contaminated with urine and feces and is 

 unfit for drinking. The greatest difficulty, however, is that 

 active mice will continually run through any open water 

 dish, very frequently splashing water upon their fur. Often 

 they become chilled and contract pneumonia, which usually 

 proves fatal. 1 



For these reasons a closed drinking-water supply is best. 

 A bottle fitted with a rubber cork pierced by a glass tube is 

 most satisfactory. The glass tubing should be drawn to a 

 nipple and the end smoothed in the flame, because water 

 will drip through a large opening. This provides constantly 

 a hanging drop which is licked by the mice when they 

 desire it. 



Records. Every animal should be numbered and registered 

 with regard to individual number, sex, description, known 

 recessive characters, parents, date of birth, and often disposi- 

 tion and date. 



A card index should be kept, bearing the numbers of the 

 cages upon the guide cards and a card filled out for each 

 animal with data on individual number, sex, purpose and 

 date of mating, and cage number. This should be filed at 

 the proper place within the index. 



When a female becomes pregnant, she should be given a 

 separate cage, because, with other mice in the cage, some 

 mothers become excited and kill their young. New-born 

 mice are often killed by males or more often still by other 

 females in the cage. Date of birth, record number of the 

 father, and information concerning the young not yet reg- 

 istered may be jotted down upon the card of the mother. 



Numbering. A satisfactory system of marking mice for 

 identification purposes is to punch the ears with a chick 

 punch. The following simple system of position marks is 

 used almost exclusively by American geneticists. The first 



1 The practice of providing open water dishes may have occasioned the state- 

 ment of Aristotle concerning the white mice of Pontis that if they drink water 

 they will die. 



