SECT. 4] HEAT-PRODUCTION OF THE EMBRYO 



727 



and in the embryo plus placenta falls. Some figures for placenta 

 weight in rabbits are included on the graph. Evidently the placenta 

 circulation fills up with blood before the true embryonic circulation 

 has had time to develop very far, and in the early stages the blood- 

 vessels in the embryo form only a small part of the total placental 

 circulation. All these facts have an obvious importance with relation 

 to foetal respiration. Cohnstein & Zuntz in their paper gave a full 

 bibliography of the earlier work 

 on blood-volume in newly born 

 infants and the young of ani- 

 mals. They also dealt with the 

 changes in the blood following 

 birth, the foetal blood-pressure, 

 the foetal pulse frequency and 

 circulation rate, using Lud- 

 wig's Stromuhr. They did not 

 relate any of these determina- 

 tions very closely with the age 

 of the embryo. 



Their most important work 

 was done on the blood-gases of 

 the embryo. They determined 

 the oxygen and carbon dioxide 

 content of the umbilical artery 

 and vein, and found what 

 change took place during an 

 interval of 24 minutes. From 

 the resulting differences they 

 did not themselves calculate 

 the respiratory quotient, say- 

 ing that a much greater number of " Doppelanalysen " would be 

 required, but this has often since been done from their figures (e.g. by 

 Murhn) ; in one of their experiments it works out at i-6, in the other 

 at 1-04. They calculated from their data the amount of oxygen used 

 and carbon dioxide given out over a definite time per unit weight 

 (metabolic rate), and obtained in the case of a sheep embryo of 

 1300 gm. the figure of i-i6 c.c. oxygen per kilo per minute. Com- 

 paring this with Reiset's figure for the adult sheep, of 5-8 c.c. oxygen 

 per kilo per minute, they concluded that the embryonic metabolic 



NEII 47 



10 20 30 40 



Weight in grams rabbit embyros 

 Blood vol. Inyo fo In placenta +foetus 

 of embryo s® " " only 



weight (• In foetus only 



Fig. 161. 



