368 ZOOLOGICAL POSITION OF THE ALBINO RAT. 



There are other differences in the various viscera, which, though not so 

 conspicuous, may be biologically of great importance. Further, the albino has 

 become docile and easy to handle and has very largely lost its habit of gnawing. 



We are inclined to regard these alterations as the result of domestication 

 and one prime experiment which needs to be made in this connection is to allow 

 the albinos to run wild for some years and observe such changes as may occur. 

 For this we need the use of an island where the albinos may be set free, thus 

 giving the opportunity for following the effects on them of a return to the wild 



life. 



As has been said , the origin of the albino strain must have been from one or 



more mutants or sports, and groups of albinos were probably obtained not only 



by the direct pairing of two mutants, but by the method we now designate as 



"extraction." Thus if the hybrids from gray and albino parents are bred 



together, the albino character appears in the next generation in a given proportion 



of the young. Albinos thus obtained are called "extracted albinos." 



While all such albinos breed true as to color, the composition of the germ 

 elements or gametes is undoubtedly different among them in accordance with 

 their ancestry. This can be illustrated by the studies on coat color. 



The current analysis of color development in animals leads to the view that 

 it depends on a chromogen — or color-producing substance — a color ferment 

 (or tyrosinase) which by its action on the chromogen gives rise to the pigment 

 proper and a so-called color pattern factor — which determines the distribution 

 of the pigment — as a rule in accordance with some general scheme. 



It appears very probable (Saunders) that the albino lacks only the color 

 ferment. Thus the albino, according to this view, still carries the chromogen 



and also the color pattern factor. 



It has been noted that this last may even show itself in the albino by the 



character and distribution of the white hairs (Mudge). 



The gametic dissimilarity of various albinos in respect to color is further 

 shown by the fact that in breeding tests (Mudge) with pigmented mates albinos 

 extracted from ancestors with characteristic differences in pigmentation will 

 reveal their origin by producing characteristically pigmented descendents, the 

 markings of which can be predicted. So much for the case of color. Other char- 

 acters, however, may be studied in the same way. 



In the case of some other characters, such as body length or brain weigh , 

 Dr. Hatai has been able to show that if these depend on a very large number ot 

 determinants, it may be possible to retain the theory of alternate inheritance in 

 relation to them, even in the face of the fact that the descendents apparently show 

 a blended inheritance without evident segregation. . 



Whether such characters are to be regarded as of the same class as coat co or, 

 is a problem by itself. What we are immediately concerned with is the game 1 

 composition of the general population of the albino rats as they appear in o 

 colony to-day. 



