Postnatal Changes in the Oxygen Capacity and Dissociation Curve of the Blood of Lambs *

Observations on the form and position of the oxygen dissociation curve of the bloods of fetal sheep indicate that they are uniform in character and position from the 60th through the 116th day postinsemination, though placed far to the left of similar curves prepared with bloods from normal adults.' Curves prepared with bloods from fetuses 117-121 days postinsemination may be of the earlier form and position or be placed slightly to the right, i.e., the period marks the beginning of the transition from the earlier fetal toward the adult type of dissociation curve. The curves of bloods of older fetuses, 122nd day postinsemination to the end of gestation at about 145-150 days, appear always to be situated to the right of the earlier curves characteristic of the first four months of the gestation period, but the most advanced curve obtained from the blood of a full-term fetus delivered by caesarian section was still far to the left of the limits of the area in which the curves of normal adults fall. Clearly the transition from the fetal type of oxygen dissociation curve to that of the adult sheep must be completed in the postnatal period. The object of the experiments to be reported here was to determine: (i) the rate at which this transition takes place postnatally; (ii) when it is completed; and (iii) to discover circumstances that might be associated with its genesis and rate.