64 HELEN DEAN KING AND HENEY H. DONALDSON 



huddled together in a corner of the cage, trembling and click- 

 ing their teeth incessantly, or they tried to hide under the 

 bedding material. If the cage door was opened they were 

 apt to jump directly at one 's face in a frantic effort to escape. 

 Food put into the cage, no matter how hungry the rats might 

 be, was never touched until the workers in the colony had 

 departed for the day. These rats were very quarrelsome, 

 and some of them were killed and eaten by the more powerful 

 individuals. 



The wooden cages that housed these rats had to be pro- 

 tected at all vulnerable points with heavy wire or iron sheet- 

 ing, as the rats were constantly seeking a way to escape. 

 If they succeeded in loosening the protective covering at any 

 point they would gnaw a large hole through the thick wood 

 of the cage in a few hours. When trapped after such an 

 escape they showed excessive fright for a considerable time. 

 It was several months before these rats became sufficiently 

 accustomed to their new environment to render the work of 

 caring for them and of taking necessary records other than 

 an arduous task. 



Miller ('11) has given an account of the mating behavior 

 of gray rats in captivity that is in accord with my own ob- 

 servations. This subject, therefore, need not be considered 

 here. Miller also noted the fact that wild gray females are 

 prone to kill and devour their young at or shortly after 

 birth a tendency which led to the destruction of a number 

 of litters in our colony also. As already stated, it became 

 necessary to remove the young of the first generation from 

 the cage as soon as they were discovered and to give them 

 to an albino female to rear in order to obtain any litters 

 with which to start the strain. 



Since it would have been of distinct advantage in working 

 with these rats of the first generation to have them tame 

 enough to be handled without the use of ether or of forceps, 

 as are albino rats, an attempt was made to tame some of the 

 young that were suckled by albino foster mothers. After 

 the rats were a week old they were taken from the nest each 



