The relationships between six of the seven allotypes or families of allotypes (a, b, c, d, f, g) described in the preceding paper, have been studied from the standpoints of (1) their antigenic specificities, (2) their mutual influence on the limitation of their respective frequencies, and (3) their genetic control.

Although the six different allotypes (or families) react quite differently with the rabbit antisera, at least five of them react identically with a guinea pig antiserum. Therefore, a large portion of the antigenic specificity of these allotypes, distinct from their allotypic specificity, is uniform in all the individuals of the rabbit species and is termed for this reason "isotypic specificity."

In the early period of the rabbit's life, allotypes may be found in the serum, which are not determined by the genotype of the individual, but are directly transmitted by the mother. The allotypes of the antigenic species of globulin studied in this paper, which were synthesized by the young animal, did not appear in its serum before a certain period of time.

Allelic relationships between the genes which control allotypes were indicated by, (1) the absence of certain kinds of groupings of the allotypes, which limits the number of allotypic formulas in the population sample studied, (2) dosage effects, the concentration of certain allotypes (drawn from the penetration of the zones in gel tubes) being smaller in supposed heterozygotes than in supposed homozygotes, (3) the results of the analysis of the sera of a number of rabbits and of their parents.

Eight of the different antigenic substances studied in this paper (allotype e excluded) appear to be allotypic forms of what would have been considered to be a uniform protein antigen. They may be classified as follows: a first group which contains two allotypes b and d and a family of two allotypes c and c' apparently controlled by three allelic genes b c d, c and c' being controlled by the same gene; a second group which contains two allotypes a and f and a family g, g' apparently controlled by three allelic genes a f g. There are reasons to believe that this list is not complete, especially in the b c d group.

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