38 THE INHERITANCE OF COLOR IN MICE. 



THE INHERITANCE OF SPOTTING. 



Spotted forms exist in all the various color varieties of mice. Such 

 spotted or piebald animals possess an amount of white varying from a few 

 white hairs to a condition in v/hich pigment occurs in the eye alone, all the coat 

 being white. Spotting is at present one of the least-understood color phenom- 

 ena, and further research is necessary before the correctness of any hypothesis 

 concerning it can be proved. Nevertheless, it seems advisable to consider the 

 physiological nature of spotting and to attempt to eliminate such theories as 

 may be shown, even with our present imperfect knowledge, to be incorrect. 

 As stated in the first part of this paper, present chemical knowledge leads us to 

 the belief that all mammalian pigments are melanins. 



Superficially, spotting appears to be partial albinism, and the question 

 naturally arises as to whether it really is due to the same cause or causes that 

 produce albinism, such cause or causes manifesting their presence in a lesser 

 degree or in a mosaic condition. 



Experimental evidence does not support a theory which postulates the 

 common origin of white produced by spotting and that produced by albinism. 

 If spotting is partial albinism we should expect, when spotted animals are 

 crossed with albinos, that only spotted or albino animals would be obtained. 

 Among the results observed by various investigators, none show better the fal- 

 lacy of this point of view than the classic experiments of Darbishire (1902) with 

 crosses of spotted waltzing mice and albinos of gray (black agouti) ancestry. 

 The appearance of uniformly pigmented animals in the first generation of this 

 cross proved conclusively that the processes producing the white of spotted 

 coats and the white of albinos are not only non-identical, but are fundamen- 

 tally different. 



Since a difference in origin of these two types of white exists, the next 

 matter of interest is to find out whether the difference lies in the qualitative 

 chemical make-up of the two whites or in the nature of the distributive proc- 

 esses which allow them to appear in the hair. 



Experiments bearing upon the qualitative nature of the two types of white 

 have been made by Mudge (1909a) on piebald (spotted) and albino rats. He 

 treated the pelage of animals of both these varieties with chemical agents cal- 

 culated to provide an oxidizing substance which might act upon the chromogen 

 in the white portions of the coat, if such a chromogen were present there. He 

 found that the white hairs in both categories of animals became yellow, both 

 reacting equally to the agent provided. A few months after the publication of 

 his work on rats he obtained similar results in piebald and albino mice, by 

 slightly varying the composition of the agent used. 



The writer does not possess sufficient knowledge of chemistry to comment 

 upon the ultimate value of the work done by Mudge, but in absence of contrary 

 evidence it seems that his work, especially as it deals with the very types that 

 we are considering, is worthy of confidence and forms a suitable base from 

 which to draw conclusions. 



