342 BIOCHEMICAL GENETICS 



material. If the infective theory is correct, then one might expect that, if one trans- 

 plants into a host that cannot produce pigment of certain colors, infected cells would 

 be obtained that would give pigment on a white background, but the pigment would be 

 of the wrong color. It appears to be a more discriminating method than the one that 

 you tried in which a positive result is required in order to give you something on which 

 to base a conclusion. 



Dr. Owen : Have you followed this reaction colorimetrically as well as by oxygen 

 consumption ? 



Dr. Foster: No, but I think we can now by dealing with material incubated 

 inside dialysis membranes. Although we have not done it because of other work, it is 

 certainly a very worthwhile thing to do in order to have some information about 

 intermediate steps along the way. 



Dr. Coleman: We have used a different assay, in conjunction with those already 

 described, in studying this problem. 213 This assay involves the measurement of the 

 amount of incorporation of radioactive tyrosine into the pigment granules. This assay 

 has been found sensitive enough to distinguish clearly all the alleles of the C locus, a 

 distinction not possible with the manometric method. Otherwise our results are 

 essentially the same as those of Dr. Foster. Our studies with the pink eyed black 

 mouse (BBCCpp) suggest that pink eye decreases the amount of tyrosine incorporated 

 into actual pigment in contrast to the increased tyrosine oxidation associated with the 

 pink eye gene as measured manometrically. These observations suggest that pink eye 

 causes tyrosine to be oxidized faster but to some product which is not melanin. This 

 demonstrates the value of using more than one assay method as suggested by Dr. Owen. 



As for the yellow mouse our work indicates that less tyrosine is incorporated into 

 pigment in this genotype than either of the normal brown or black genotypes. Both 

 studies in vitro and in vivo indicate that tyrosine is the normal precursor to yellow pig- 

 ment. No evidence has been found which would implicate tryptophan or any other 

 amino acid as a precursor to this kind of pigment. 



Dr. Herzenberg: The kind of experiments that Dr. Silvers carried out in animals 

 which are inbred could be carried out in other animals as well, particularly chickens 

 and other birds by making them tolerant to the donor of the skin with which they are 

 willing to work. If Dr. Nalbandov is interested in carrying this out, I am sure he 

 could do it. 



Dr. Heston: There are strains of chickens at the Regional Poultry Laboratory at 

 East Lansing that may be inbred enough for your experiments. 



Dr. Silvers: Dr. Billingham and I have tested some of the inbred lines of chickens 

 maintained at East Lansing, Michigan by skin graftings and have not found any 

 histocompatible strains as yet." However, we are now testing some more of these lines. 



Dr. Schaible: With regard to transplantation experiments involving pigmented 

 and unpigmented regions, the chicken has another drawback in that there are no 

 mutants which produce adult spotting patterns like those found in mammals. In 

 chickens, melanocytes seem to be able to proliferate until they occupy all feathered 



