234 



The Journal of Heredity 



factor of sooty yellow rabbits (e) make 

 an interesting contrast between two 

 factors of class 2a. In the former case, 

 as we have seen, Onslow demonstrated 

 that an enzyme inhibitor was j^roduced, 

 in the latter he was simi)ly unable to 

 demonstrate ])eroxidase, indicating a 

 reduced quantity or potency as com- 

 pared with blacks. The following table 

 shows the effects produced by these 

 factors when added to those of a solid 

 black rabbit (aaEE) : 



oaEE AAEE 



Back Black Black ticked with yellow 



Belly Black White 



aaee AAee 



Back Sooty yellow Clear yellow 



Belly Black White' 



The case can readily be understood if 

 we suppose; first, that both enzymes 

 I and II are strong on the back but 

 feeble on the belly in all rabbits due to a 

 regional differentiation. We will sup- 

 pose that enzyme I is below the yellow 

 threshold on the belly. Second, we will 

 suppose that factor A determines the 

 production of an inhibitor with the 

 same subtraction effect on enzyme II 

 everywhere, while factor e determines a 

 general jjroportional reduction in rate of 

 production of enzyme II. On this 

 basis it follows that factor A produces a 

 partial inhibition of black on the back, 

 revealing yellow but a complete inhibi- 

 tion of black on the belly where, how- 

 ever, only white can be revealed. Fac- 

 tor e reduces black on the back suffi- 

 ciently to permit yellow to predominate 

 in com]jetition while on the belly, where 

 there is no comjjetition from yellow, 

 what little of the black producing en- 

 z>Tne I-II is jjroduced is fully effective 

 and black, or at least blue, results. 



Class 2b. — The factors which reduce 

 the intensity of black areas in skin, fur 

 and eyes without affecting red areas form 

 a clearly defined class. The br(jwn-eyed 

 chocolate mice, guinea-])igs and ral)bits; 

 the jjink-eyed pale sepia f)r "lilac" 

 mice, guinea-])igs and rats, and the 

 red-eyed rats of similar coat color^^ 



differ from blacks by factors of this 

 class. Among the larger animals the 

 difference between liver-colored and 

 black dogs seems to be of this kind. 

 Probabh' chestnut and liver-colored 

 horses differ from ba>'s and blacks by 

 such a factor. All of these factors are 

 recessive. In the pink-eyed mice, 

 guinea-pigs and rats it is remarkaVjle to 

 what an extent black is diluted without 

 bringing out any distinctly reddish 

 tinge although in red regions of the fur 

 as in the agouti band of gray varieties 

 the red appears in full intensity. There 

 is evidently a different sort of reduction 

 of enz}'me II from that in the sooty 

 yellow rabbit. A normal quantity of 

 enzyme II but reduced potency in 

 some other way would seem to be re- 

 quired in class 2b. 



SIMULTANEOUS EFFECTS 



It has been assvuned so far that factors 

 act only on one or the other of the hypo- 

 thetical enzymes I and II. In the great 

 majority of cases this is satisfactory but 

 it is not impossible that a factor may 

 influence both enzymes in the course 

 of development. In fact the writer 

 will soon publish e\'idence on one such 

 case in guinea-pigs. Tri-color male 

 guinea-pigs of many different stocks 

 agree in showing a slightly greater 

 average area of color as opposed to white 

 than their sisters, and they also show 

 relatively more black as opposed to red. 

 Maleness seems to determine a higher 

 level of both enz\TTics I and II as re- 

 gards pattern. The effect on color is per- 

 ha])s due rather to a general metabolic 

 difference in the cells of males and fe- 

 males early in ontogeny than to any 

 specific modes of action on the two en- 

 zymes. The same may be true of cer- 

 tain coat patterns in which it seems 

 necessary to suppose that the level of 

 enzymes I and II is raised or lowered 

 simultaneously in some resjject by 

 regional differentiation. We have cited 

 the cases of the rabbit, mouse, and 

 guinea-] )ig in which it was found con- 



" These red-eyed rats first described by Castle C1914, Amer. Nat.) under the name of yel- 

 lows must not be confused with the red-eyed rats described by Whiting (loc. cit.). In the 

 former yellow pigm?nt is unaffected and to a large extent gives the color to the fur in agoutis, 

 owing to the great reduction of black. In the latter, yellow is reduced to white, while black is 

 only slightly affected. 



