Electrocardiograms and morphological alterations of the heart were observed in detail in several stages of the previous experiment. Electrocardiograms of the bipolar lead (A-B lead, same as the second limb lead in man) and the precordial unipolar leads on the right and left ventricles were recorded at sea level at the third week after birth before exposure, and at the eleventh week after exposure. Thickness of ventricular walls in the transection of necropsied hearts, running parallel with the

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... oronary groove (Sulcus coronarius) at the central part of the heart, were measured at the eleventh, the fifteenth and the twenty-second weeks after birth. Differences in measurements among the altitudes are discussed statistically by the analysis of variance. In addition, the histological structure of the myocardium obtained at the eleventh week after birth was examined. The results obtained were as follows: No differences among the five groups in measurements of electrocardiogram were recognized statistically, but the qR type of