The cause of congenital malformations remains unexplained. It is not known whether they are due to defects in the germ plasm of the parents or to injury of the growing embryo. In order to throw light on the question, an investigation of a series of families, each possessing a defective child, has recently been made. Among the characteristics studied in these families was the birth order of each normal and of each malformed child. An analysis of the data on this point forms the basis for the present report.
Still1 has studied the birth rank of malformed children seen by him in private practice. He concludes that congenital heart disease, congenital pyloric stenosis and various other defects appear more often in the first born than in the later born.
Macklin2 has studied the place-in-family in a series of malformed individuals reported in the literature. Contrary to Still, she