334 



BIOCHEMICAL GENETICS 



eumelanin-producing cells by a postulated infective agent derived from pigmented 

 melanocytes, 94 • 95 • 96 • 97 • 98 and (2) pigment spread is simply due to the actual migration 

 of melanoblasts or melanocytes. 



The fact that pigment spread can be initiated by seeding a white spot with cellular 

 homografts of dissociated epidermal cells including melanocytes, 96 but may sub- 

 sequently bleach out spontaneously after a variable period or may be caused to bleach 

 out promptly following an immunizing skin homograft from the donor of the melanocyte- 

 containing suspension, has some important implications. The fact that albino mice 

 will permanently accept coisogenic pigmented skin constitutes strong evidence that 



Fig. 46. Principle of method of determining origin of melanocytes in annulus of 



SPREAD SURROUNDING A BLACK-IN-WHITE GRAFT IN THE GUINEA PIG. 



STRAIN A (Donor) 



STRAIN B 



PRIMARY HOST 



Fi(AxB) Hybrid 



-Pure epidermal graft 

 containing melanocytes 

 from annulus of spread 



SECONDARY HOST 

 'Strain A sensitized against 

 strain B by an Fj or B homograft 



melanin per se is not an isoantigen. Thus if the pigment spread initiated by homologous 

 melanocytes is the result of a progressive infection, it follows that homologous melano- 

 cytes must infect the postulated amelanotic melanocytes with transplantation antigen (s) 

 as well as with a capacity to synthesize melanin, unless part of the melanogenic 

 machinery happens to contain a transplantation antigen. 



The general biological implication of the infection theory suggests that differences 

 between the various melanocytes of a single guinea pig are due to cytoplasmic rather 

 than to nuclear differences. Furthermore, if proven, it would represent the first 

 example of an autonomous cytoplasmic component that gives cytoplasmic inheritance 

 in a mammal at the somatic-cell level. 



