The bloods of thirty-eight newborn infants were tested for the agglutinogens M and N to determine whether these substances are established at birth. Of these thirty-eight babies, two were seven-months and two eight-months prematures. The bloods of the mothers and, in all but seven cases, those of the fathers were also tested.

To determine the constancy of the types appearing in the newborn, tests were made again on them from six to twelve days after birth, from three to four months after birth, and when they reached fifteen or sixteen months of age. Because one investigator has reported the appearance of additional A and B agglutinogens after birth it was thought advisable to study these groups in conjunction with the M and N types. Consequently, all infants and adults were tested for these properties.

The M and N types were found to be established at seven months; in all cases, the types appearing in the newborn were those theoretically to be expected from the parental matings involved. There were no exceptions to the theory that the agglutinogens M and N are inherited as a single pair of allelic genes.

Subsequent tests indicated that the types are not only established in the foetus at seven months but are probably completely developed, for no changes in typing were noted up to fifteen and sixteen months of age.

The same results were obtained from a study of the agglutinogens A and B in newborn infants. No exceptions were found to the Bernstein theory and no changes were noted in grouping.

Therefore, it may be concluded that the hereditary agglutinogens M, N, A, and B are completely developed at the seventh month of pre-natal life, since no exceptions to any of the rules were found and the types and groups remained constant.

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