478 BIOLOGY OF THE LABORATORY MOUSE 



of the ear. By this system it is possible to number, on the ears, from i to 99 

 for individual identification. The complete serial number of each animal is 

 kept on the individual card. 



The animals are marked when they are weaned and breeding pens are 



usually made up at this time. Each side of the boxes has sufhcient space for 



six adult animals and thus five females may be mated to each male in strains 



where the animals show high fertility. Matings in 



LEFT EAR RIGHT EAR • , , , • > • , u 4^u \/ • <. 



mbred strams of mice are always brother X sister 



r o\ '^ ) unless a son is mated to its mother or a daughter 



"^' — '^— ^ '■ to its father. Cousin matings should never be made 



e/^ o) if one wishes to maintain a homozygous stock. A 

 — '-■ practice which will save considerable time eventu- 

 CN /'j ally is to keep a small pedigree chart for every strain 



^ -Jiy ^- on which every individual is recorded which has 



e/'~^ been mated. The development in any animal of 

 ~._y 4. any desired character or condition should be noted 

 C/^^ on this chart. After every few generations the best 

 ,^_^ 5. line may be selected from which to continue the 

 C/^~\. stock. Litters or sub-lines which are not wanted 

 .,^^^ 6. should be discontinued. Unless some method for 

 CjS~^ selecting the matings is used, the strain may 

 ^^y J eventually consist of sub-lines which differ markedly 

 C>— V from each other. If the development of different 



y g sub-lines is desired the chart will aid in assuring the 

 C^-. worker that all lines are being continued. 



J On the individual female card are recorded the 



^-^^ number, color and sex of each mouse. Space is also 



V ) provided for the strain or line, the inbred generation, 



"*~^' date of birth, death, development of spontaneous 



Fig. 172.— -Earmark- tumor, age at death or development of tumor. The 

 ines for individual iden- ,. .- ^, . , , •, , ■ ■ u u ^^ 



.,? . . ., pedigree ot the animal may be written at the bottom 



tincation; units on right ^ <=' 1 i- 1 



ear tens on left ear ^^ ^^^ ^^^'^ ^^^ ^^^ mating and breeding box number 



inserted. Space has been provided to enter data for 

 twelve litters. In successive columns, from left to right, may be given for each 

 htter: the generation, ledger number, date born, number born, born dead, 

 weaned, females, males, age of mother at the birth of each litter and the num- 

 ber of days between litters. These cards may be altered to catalogue any 

 information that a worker may want in his investigations. (Sample card will 

 be supplied on request.) The male card may be a ruled 4X5 library card 



