WRIGHT 



There are three points in tlie dia- 

 gram (Fig. 1) at which physiological 

 processes may affect color-production 

 independently, viz., by influence on 

 chromogen, on enzyme I, and enzyme 

 II. In the first two cases color should 

 be modified regardless of its quality. 

 But as there is as yet no experimental 

 evidence that genetic factors deter- 

 mine variations in the chromogen ele- 

 ment it will be convenient at present 

 to consider all such cases as due to 

 influence on enzyme I. 



The relations between black, red 

 and white in this scheme are obvious. 

 Inhibition of enzyme II when enzyme 

 I is present gives red. Inhibition of 

 enzyme I gives white regardless of 

 whether enzyme II is present or not. 

 The intergradiuCT colors must be looked 

 upon as resulting from reductions of 

 various kinds in the activity of the 

 enzymes. We have recognized two 

 distinct types of intergrades between 

 black and red, the coarsely granular 

 type of bays and sooty yellows, and 

 the finer type of chocolate browns. 

 A mere reduction in quantity of en- 

 zyme II may perhaps be thought to 

 result in an intermingling of black and 

 red granules as one or the other of the 

 respective enzymes chances to pre- 

 dominate, while a uniform reduction 

 in potency in some other way not 

 involving a reduction in quantity may 

 give the chocolates and the pale 

 browns of the pink-eyed rodents, in 

 which there seems to be little more 

 tendency for red to win in competi- 

 tion than in intense blacks. Similar 

 relations with respect to enzyme I may 

 account for the differences between 

 the maltese and sepia types of dilution 

 of black and the correlated light red 

 and cream types of dilution of red. Of 

 course, any such definite assignment of 

 physiological effects to factors is at 

 present to be taken mainly as a means 

 of visualizing their action in our igno- 



85 



ranee of the real physiology. In order 

 to make wholly clear the relations sup- 

 posed to hold between the different 

 colors on the hypothesis, the accom- 

 panying diagram (Fig. 2.) is given. Full 

 quantity is represented by two sym- 

 bols, reduced quantity by a single 

 s\'mbol, reduced potency by a symbol 

 of small size, and complete inhibition 

 or impotency by absence of symbol. 

 X^ariations in enzyme I are given hori- 

 zontally, variations of enzyme II verti- 

 cally. 



The classification of color factors 

 which it is desired to present is based 

 primarily on the difference between 

 factors which act as if on enzyme I, 

 and those which act as if on enzyme II. 

 A secondary classification is based on 

 the mode of action. There is a wide 

 difference between factors which pro- 

 duce no effect in parts of the coat 

 though with maximum effect in other 

 parts, i.e., bring out a pattern, and fac- 

 tors which produce the same effect 

 throughout fur, skin and eyes. In the 

 former case increase in the array of 

 factors causes extension of the pattern; 

 in the latter whatever pattern may be 

 present tends to be stationary on in- 

 crease in the array of factors. There is 

 instead a further general change in in- 

 tensity. The coarsely granular types of 

 intergrades should perhaps form a 

 third subclass in each main class, but 

 for the present they are most con- 

 veniently put with the pattern fac- 

 tors. They can be considered as deter- 

 mining a fine pattern within the 

 individual hairs. 



CLASSIFICATION OF COLOR FACTORS 



1. Factors which affect distribution 

 and intensity of color, largely irre- 

 spective of the kind of color. (Act as 

 if on enzyme I.) 



{a) Factors which affect the dis- 

 tribution of color in contrast with 

 white. 



