518 THE PHYSIOLOGY OF REPRODUCTION 



of the product of conception. To a certain extent diffusion of 

 oxygen takes place from mother to foetus, as it has been proved, 

 by experiments in asphyxia of the mother, that the direction 

 in which oxygen goes across the placenta depends on the tension. 

 Whether there is also a gas-secretion by the trophoblast is 

 unknown. 



With regard to the foetus, Pfliiger argued on theoretical 

 grounds that the oxidation processes were inconsiderable, and 

 the oxygen intake small. This was confirmed experimentally 

 by Cohnstein and Zuntz. 1 More recently, however, Bohr 2 

 has shown by more convincing experiments that in the later 

 stages of pregnancy the foetal guinea-pig consumes at least as 

 much oxygen as the mother. The actual figures which he ob- 

 tained were 462 c.cm. for the mother and 509 c.cm. for the foetus 

 per kilo per hour. He has also shown that the foetal respiratory 

 quotient is unity, indicating that carbohydrates are the source 

 of energy. The same has been found in new-born puppies 

 before suckling (Murlin 3 ). It is well to remember that Bohr's 

 experiments refer only to the foetus in the later stages of de- 

 velopment, and that they entirely leave out of account the 

 placental metabolism. 4 



The high consumption of energy in the foetus, which differs 

 from the adult in losing little heat by radiation from the skin 

 surface and lungs, must be due to the intensive growth of the 

 embryo (see Chap. X., p. 434). 



1 Cohnstein and Zuntz, " Untersuchungen iiber das Blut, den Kreislauf, 

 and die Atmung beira Saugetierf otus, " Pfluger's Arch., vol. xxxiv., 1884. 



2 Bohr, "Der Respiratorische Stoffwechsel des Saugetierembryos," Skand. 

 Arch.f. Phys., vol. x., 15100. 



3 Mnrlin, "Protein Metabolism in Development," Amer. Journ. of Phys., 

 vol. xxiii., 1908-9. 



4 In the later stages there is a wide distribution of glycogen throughout the 

 tissues of the foetus, and the foetal liver has assumed its glycogenic function. 

 It is scarcely justifiable to extend Bohr's results to the early stages of 

 pregnancy, when the placenta probably takes a leading part in embryonic 

 development. It may be that at that time also glycogen is the source of 

 energy for the placenta in Rodents, but it cannot be so in Ruminants. In 

 their placentae glycogen is found only in traces, while fat is in consider- 

 able amount. Hence we cannot assume that the energy is derived from 

 the combustion of carbohydrates until experimental evidence has been 

 obtained. 



