NUTRITION OF THE EMBRYO 1135 



kind must be at its lowest ebb. Consciousness, if it exists at all, 

 must be dull and muffled. And if motor impulses are discharged 

 from the cortex, the psychical accompaniments of such discharge are 

 doubtless widely different from those which we associate with 

 voluntary effort. 



It is a remarkable fact that this functional calm, broken only by 

 the beat of the heart, is accompanied by a relatively intense 

 metabolism of the same order of magnitude as that of the adult. 

 In the hen's egg at all stages of development the consumption of 

 oxygen and production of heat (per kilogramme and hour) are the 

 same as in the adult hen. The oxygen consumption and carbon 

 dioxide production of pregnant guinea-pigs were determined before 

 and during compression of the umbilical cord of a foetus, and a dis- 

 tinct diminution was observed when the respiratory exchange of the 

 foetus was eliminated. From the results of a number of observations 

 it was calculated that the carbon dioxide produced by the mother 

 was 462 c.c., and by the foetus 509 c.c. per kilogramme of body- 

 weight per hour (Bohr and Hasselbach). A similar comparison 

 between women before and during pregnancy never showed any 

 diminution in the respiratory exchange reckoned on the unit of body- 

 weight in the pregnant condition. In one case, indeed, and that 

 the most exactly observed, there was an increase in pregnancy. 

 Now, in the pregnant woman a considerable part of the increase of 

 body-weight is due to the amniotic fluid, in which, of course, meta- 

 bolism does not go on. It is evident, then, that in the human fcetus 

 also the intensity of metabolism is at any rate not of a lesser order of 

 magnitude than in the mother, in spite of the much smaller amount 

 of muscular contraction taking place. The heat production of mother 

 and child together has been directly estimated in several cases in a 

 respiration calorimeter provided with a bed just before parturition 

 and just after it. After parturition the heat production of the 

 mother was also separately determined. From the difference it was 

 concluded that the heat production of the child per kilogramme 

 of body-weight per hour is approximately two and a half times 

 that of the mother under the same conditions. (Carpenter and 

 Murlin.) 



The foetal heart beats at the rate of about 140 times a minute at 

 full term.* The blood-pressure in the umbilical artery of the 

 mature embryo (sheep) varies from 60 to 80 nun. of mercury; 

 but at the beginning of the aorta it will be more. The pressure in 



* It has not been finally determined whether the rate of the heart varies 

 with the size or, what probably comes to the same thing, with the sex of the 

 foetus. As we have seen, the variation of the rate in the adult with the size 

 of the body is associated with a corresponding variation in the metabolism 

 and heat-loss, which are proportionally greater in a small than in a large 

 animal. If this is a causal connection we should not expect that in the 

 embryo in utero, where the conditions as regards heat-loss are entirely different, 

 such a relation should exist, at any rate within the same species. 



