22 LABORATORY MOUSE 



to normal pigmentation, chinchilla {157), and extreme dilu- 

 tion (39). 



Complete albinism or one of its allelomorphs in which 

 very little pigment is produced is known to occur in fish, 

 birds, and most species of mammals, including man. 



Extreme Dilution (c H ) 



Mr. J. E. Knight brought into my laboratory a young male mutant 

 mouse which he had captured in a corn crib. . . . This animal . . . gave 

 the appearance of being an ordinary black eyed white in which the hair 

 was apparently very slightly stained or dirty. — Detlefsen, 1921. 



The above description of the extreme-dilute mouse (see 

 Fig. 13) is quite accurate (39). These animals vary in shade 

 but are always a dirty white color. This is apparently due to 

 a complete suppression of yellow and an almost complete 

 suppression of black and brown in the coat. I have found 

 that intense pigmentation persists in the ears, eyes, upon 

 the tail, and to a lesser degree upon the feet. 



In the possession of pigmented extremities this mutant 

 resembles Himalayan albinism of the rabbit, and indeed its 

 determiner occupies a corresponding position among the 

 alternative forms of the albino gene. 



Upon superficial examination of extreme dilutes it is im- 

 possible to distinguish blacks, browns, agoutis, non-agoutis, 

 and so forth. Closer inspection and continued handling en- 

 ables one to differentiate blacks from browns by the shade 

 of pigment upon the ears. These distinctions may be con- 

 firmed by clearing the irida? in xylol. Such prepared iridse 

 show normal black or chocolate pigmentation according to 

 whether the animal is genetically a black or a brown. 1 



Chinchilla (c ch ) 



Thus the first generation of hybrids (between wild gray house mice 

 and fancy albinos) consisted of 342 mice, of which 329 were gray, seven 

 yellow and six chinchillas. — - Schuster, 1905. 



1 An old fancier in the fourth edition of Fancy Mice says: "Occasionally impure 

 breeds and strains (of albinos) are raised in which there are black ears, eyes, and 

 feet. . . ." This may indicate extreme dilution, which being a dominant allelomorph 

 to true albinism might carry it as a recessive and continue to produce true albinos 

 generation after generation. 



