346 IMMUNOLOGICAL STUDIES 



reasonable to assume that the specific structure of any antigen is 

 represented by some special feature of a corresponding gene. For 

 example, this feature can be considered a structure complemen- 

 tary to that of the antigen (see p. 365). In this sense all antigens 

 would be regarded as preformed in the fertilized egg. At the same 

 time, the actual appearance of the antigen would be epigenetic, 

 dependent upon the time and extent of action of the particular 

 gene. It is also possible that all antigens are present, but some 

 in undetectable amounts, along with their determinant genes (or 

 other self-reproducing cytoplasmic body ) at the start of develop- 

 ment. In either case the processes involved in the determination 

 and differentiation of the various tissues and organs would be as- 

 sumed to entail concomitant activity of specific genes, determin- 

 ing also the formation of characteristic antigens of the tissue or 

 organ. 



Despite the inability to prove complete absence of an antigen 

 one may, nevertheless, raise the question of whether or not spe- 

 cific "organ" antigens can be detected before the time of visible 

 differentiation. The evidence in the above-cited investigations, 

 although rather incomplete, would answer this in the affirmative. 

 For example, specific antigens of lens, brain, spleen, and heart 

 have been detected at stages well in advance of the differentia- 

 tion of the particular organ. It has also been reported (Woerde- 

 man, 1953a,b, 1955) that lens antigen can be induced to appear 

 in extracts of presumptive lens ectoderm by incubating in the 

 presence of extracts of optic vesicle. 



A large fraction of the antigens of adult tissue are detectable 

 in the uncleaved egg and even in the oocyte. This appears to be 

 especially true for antigens of adult serum or serum-like antigens 

 of adult organs as Cooper ( 1946 ) showed in the first work to give 

 real impetus to the current investigations on soluble antigens. The 

 extent to which egg and adult serum have antigens in common is 

 illustrated in the work of Schechtman and Hoffman (1952) and 

 of Nace ( 1953 ) . In this work antisera that were produced against 

 whole chicken serum or the separate albumin and globulin frac- 

 tions were found to cross-react quite strongly with egg yolk. Ab- 

 sorption with yolk greatly reduced the reactivity of these antisera 



