O HELEN DEAN KING AND HENRY H. DONALDSON 



Further, speaking broadly, no such tests are now possible, 

 except perhaps in one or two instances, since the wild types 

 are either unknown or for some reason not available, and 

 consequently the data for comparison can hardly be had. In 

 the case of the Norway rat, the gray form is definitely wild, 

 depending on its own wits and exertions for its existence, 

 while the albino mutant of the laboratory has now lived for 

 many generations as a captive animal and may be fairly 

 grouped with the other domesticated animals associated with 

 man. 



Consideration at once shows that continued captivity might 

 be expected to alter the organ composition of the gray Nor- 

 way. Such being the case, the alterations which prove to be 

 similar to those now found in the Albino could be credited to 

 captivity and treatment, while other modifications in the 

 Albino not represented in the captive Norway could be re- 

 ferred to albinism. 



It was on the basis of the foregoing considerations that the 

 breeding of the Norway rat in captivity was undertaken by 

 Doctor King in 1919. Naturally, this is a very long-time 

 study which will require years for its completion. For this 

 reason, occasional reports of progress seem to be permis- 

 sible, and the following pages constitute an initial report of 

 the observations on the first ten generations of the Norway 

 rat in captivity. 



INTBODUCTION 



The purpose of this study is to determine such changes as 

 may occur in the life processes and in the body and organs 

 of the gray Norway rat when bred for a number of genera- 

 tions in captivity. In the case of the Norway rat, both the 

 wild gray race and the captive albino race are readily avail- 

 able for study. When these are compared, marked differences 

 in behavior and in the size of several organs are found. We 

 wish ultimately to determine, in the case of the Albino, how 

 far these differences may be due to prolonged captivity and 

 how far to the condition of albinism or possibly to other 



