436 THE PHYSIOLOGY OF REPRODUCTION 



digestion of proteins before their absorption by the trophoblast. 

 Further it has been shown, by means of the precipitin reaction, 

 that if egg-albumen is injected into the mother some of it passes 

 unchanged to the foetus (Ascoh ^). On the other hand, the 

 proteins of ox-serum cannot be recognised in the foetal blood, 

 even when a considerable quantity is injected.^ The reason 

 appears to be that the proteins of ox-serum resemble more 

 closely the normal serum proteins of the rabbit and are meta- 

 boHsed by the trophoblast, while egg-albumen cannot be utihsed, 

 and is passed on to the foetal circulation unchanged. Hence it 

 is probable that the normal proteins of the serum are also 

 transformed by the trophoblast into a form suitable for the 

 foetus. The exact nature of the transformation is unknown, 

 but it is not comparable with the hydrolytic processes which 

 occur in the intestine. 



Respiration. — According to Bohr,' the foetal rabbit absorbs 

 shghtly more oxygen and gives off shghtly more carbonic acid 

 per kilogram per hour than the mother. Hence the intensity 

 of the metabohc reactions is shghtly greater in foetal hfe. This 

 is directly opposed to the views held by Pfliiger on theoretical 

 grounds, and by Cohnstein and Zuntz * from their experimental 

 results. The second result of Bohr's experiments has been 

 already mentioned, viz. that in that part of the metabohsm 

 which is evidenced by the respiratory exchange, the energy 

 arises from carbohydrates. He supposes that the energy 

 liberated by the combustions, which in the adult is dissipated 

 largely under the form of heat radiated and water evaporated 

 from the surface of the body, is in the foetus used for the in- 

 crease and maintenance of the newly formed tissues ; in other 

 words, " the reactions of synthesis, which are so numerous 

 during development, are endothermic or heat-absorbing, and 

 they borrow the heat from other simultaneous exothermic 

 actions," ^ in this case the oxidation of carbohydrates. 



^ Ascoli, " Passiert Eiweiss die plaoentare Scheidewand ? " Zeit. f. phys. 

 Ghem., vol. xxxvi., 1902. This has been confirmed by the writer and Dr. W. 

 Cramer (see reference, note ', p. 435). 



2 Lochhead, loc. cit. -'' Bohr, loc. cit. 



* Cohnstein and Zuntz, " Untersuohangen uber das Blut, den Krelslauf und 

 die Atmung der Saugetierfotus," Pfluger^s Arch., vol. xzxiv., 1884. 



6 See Richet's Dictionnaire de Phyaiologie, vol. vi., Article "Foetus." 



