Another set of observations, leading to precisely the same conclusions, have been made by F. B. Chavasse of Liverpool. He terms the potential agglutination of the fœtal corpuscles by the mother’s serum, and of the maternal corpuscles by the serum of the fœtus, the “maternal threat” and the “fœtal threat” respectively, and states that there is no obvious relationship between the “fœtal threat” and eclampsia or the toxæmias of pregnancy. The inference is therefore justified that there is no transference of the agglutinating substances in either direction across the placental membranes. No chemical “immunity” is acquired, therefore, on either side, since the protection is mechanical. This agrees with the fact observed by Happ that the mother’s milk contains the same agglutinins as the serum of her blood; but these do not have any deleterious effect upon the infant, and are therefore either not absorbed at all or are destroyed in the process of digestion. The statement that the blood group of an infant is not necessarily the same as that of its mother can be amplified, for it has been found that blood groups are inherited on a definite plan, so that if the groups of the parents be known, certain predictions can be made as to the possible groups that may be found among their offspring. Many characters in animals and plants have been shown during the last twenty years to be transmitted according to the Mendelian plan of inheritance, but up to the present time very few normal characters in man have been isolated, and their manner of inheritance demonstrated, though a number of pathological conditions have been shown to conform to the theory. It is therefore of much interest to find that the inheritance of blood groups in man can be quite satisfactorily and consistently explained in Mendelian terms.