DEVELOPMENT 631 



V. Metabolism in Pregnancy. 



During pregnancy the increase in the metabolism is pro- 

 portionate to the increase in the weight of the mother. This 

 increase is due not only to the growth of the foetus, but also to the 

 growth of the uterus and mammary glands and to the formation 

 of the amniotic and allantoic fluids which are inert. Hence 

 probably the metabolism of the foetal tissues is more active 

 than that of the maternal. Experiments upon guinea-pigs 

 support this conclusion. 



It has been found by means ot the respiratory calorimeter 

 (p. 259) that the total metabolism of the mother just before 

 delivery is practically the same as that of the mother and 

 young after delivery. 



VI. The Young- Animal at Birth. 



At birth the young animal is suddenly precipitated from its 

 prolonged bath in the warm amniotic fluid where its temperature 

 has been maintained, and where it has received a steady supply 

 of oxygen and of food without any exertion on its part into the 

 chill air of the outer world where it has to secure its oxvgen 

 by the efforts of breathing, to get its food by sucking and 

 digesting and to maintain its temperature by its own meta- 

 bolism. No wonder that this sudden change proves too much 

 for the less robust, and that the mortality during the first week 

 of life is high. The power of heat regulation is not at once 

 developed, and the young animal at first tends to react to 

 the temperature of its surroundings in the manner of a 

 cold-blooded animal. In a day or two its power of 

 adaptation improves and the rate of its chemical changes 

 increases so that from this time onwards throughout the period 

 of active growth they are in excess of those of the adult (p. 266). 



VII. Fcetal Circulation. 



The performance of its functions by the placenta is associated 

 with a course of circulation of the blood somewhat different to 

 that in the post-natal state (fig. 245). 



The blood coming from the placenta to the foetus is collected 

 into a single umbilical vein, %i.v., which passes to the liver, I. 

 This divides into the ductus venosus, d.v., passing straight 



