ZOOLOGICAL POSITION OF THE ALBINO RAT. 367 



destroyer of grain and other foods and a prime carrier of the bubonic plague. 

 Because of this latter failing, both are now being hunted the world over. 



Our interest in the Norway rat in the present instance however is not due to 

 its economic or hygienic importance, but to the fact that the common albino 

 rat (M. n. albinus) kept as a pet or laboratory animal, and concerning which 

 we desire all possible information, is a strain of the Norway rat. 



This is shown by the physical characters of the albino (blood crystals, shape 

 of skull, etc.) and the fact that the two forms interbreed freely. Concerning 

 the place and time of origin of the albino strain, there is little information at 

 hand. Allusions to albino rats before the time when the Norway rat appeared 

 in Europe clearly show that there must have been an albino strain of Mus rattut 

 The only trace of this strain which has been found during the last twenty or 

 thirty years is a single skin in the American Museum of Natural History in New 

 York ( Allen) . 



By some curious slip, many of the natural histories and books of refer nee 

 speak of the existing albino as an albino of Mus rattus. This of course is not 

 correct, but owing to the confusion thus introduced, it is difficult to trace the 

 history of the present form. 



We do not know whether it had a single origin or several, or whether the 

 colonies found in Europe are directly related to those found here. 



It may be possible at some future time to solve this problem of origin, but at 

 the moment there is nothing to be said from the side of historical records. 



Judging from the way in which the albinos of other species arise, we may 

 safely assume that the present strain is derived from one or more albino mutants 

 or sports, to use the older term. These must have been captured and the albino 

 descendents protected and kept as pets, as there is nowhere to be found an 

 established colony of albinos living in open competition with the common Nor- 

 ways or with forms of Mus rattus, but all of the colonies are maintained prac- 

 tically under conditions of domestication. 



Within a few weeks, Dr. Hatai at the Wistar Institute has obtained from 

 Norway rats bred in captivity for several generations, two litters consisting mostly 

 of normal grays but one of which contained three albinos and the other, one. 

 This appears to be an unique instance of the production of albino rats under 

 laboratory conditions. 



Having followed the history of the albino rat — such as it is— and commented 

 on its zoological position, it remains to say a few words first about the effect of 

 domestication on the albino, and second, about the albino strain from a stock- 

 breeding standpoint. 



Effect of Domestication.— The albino rat differs from the wild Norway by not 

 attaining so large a size at maturity, by having become slightly shorter and by 

 having lost about 13 per cent, in the relative weight of its central nervous system 

 (brain and spinal cord). 



