A. TYLER 347 



with the serum fractions. For example, an antiserum against 

 whole serum which gave a titer of 0.0004, in terms of milligrams 

 of protein in the highest reacting dilution of the antigen, gave a 

 titer of 0.029, a seventy-fold decrease, after absorption with yolk 

 (see Nace, 1953, Table 1, p. 430). With the other antisera against 

 the various separated serum proteins (albumin, a,i8-globulin, 

 y-globulin) there was similar loss in reactivity with original anti- 

 gen upon absorption with yolk or with heterologous serum pro- 

 teins. As noted by these authors contamination of the yolk, 

 preparations with serum can be ruled out as an explanation of 

 the results. They suggest (Nace, 1953, p. 440) that the yolk pro- 

 teins may be a direct transudate from the maternal serum, or that 

 there is a mechanism for resynthesis of antigens very similar to 

 serum from degradation products of serum that pass into the 

 yolk. However, since these experiments and those of others show 

 that some reactivity for serrmi constituents remains after absorp- 

 tion with yolk, it is evident that neither explanation is satisfactory 

 unless it is further assumed that there is a selectivity as to which 

 serum proteins transudate or as to which antigens are resynthe- 

 sized. The same sort of difficulty arises in connection with the 

 presence of serum-like antigens in other tissues of the adult and 

 the developing embryo. 



An alternative explanation would be based on the suggestion, 

 presented at the beginning of this paper, that many of the chem- 

 ically different proteins, or other large molecular substances, of 

 an organism may each have identical or similar antigenic deter- 

 minant groups along with others that are characteristic of the 

 particular substance. On this basis the reaction of yolk proteins 

 with an antiserum against serum proteins would be attributed to 

 the similarity or identity of one or more of the determinant 

 groups. The great reduction in reactivity of the antiserum with 

 serum proteins after absoiption with yolk indicates that most of 

 the antibodies are directed against these common antigenic struc- 

 tures. The remaining activity after such absorption is due to anti- 

 bodies directed against determinants characteristic of the partic- 

 ular serum proteins. However, it should be emphasized again that 

 even such absorbed" sera do not necessarily detect the particular 



