464 THE PHYSIOLOGY OF REPRODUCTION 



Protein Metabolism 



In so far as the influence of the trophoblast on proteins has been 

 investigated in the placenta of the rabbit, it may be considered here. 

 It is generally accepted that colloid substances with large molecules, 

 which are not adapted for diffusion, require a preliminary transforma- 

 tion, by which the size of the molecules is decreased before they can 

 be taken up by the foetal ectoderm. But the actual observations are 

 against such a general statement. In the sheep the trophoblast can 

 absorb not only haemoglobin, a colloid, without any preliminary 

 transformation, but even enormously larger masses of protoplasm in 

 the form of cells. On the other hand, such hydrolysed products of 

 albumen as albuuioses and peptone are not present in the fresh 

 placenta, nor can any extra-cellular proteolytic enzyme be extracted. 1 

 Hence there is no evidence of a placental 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 fetus ( Ascoli 2 ). On 

 the other hand, the proteins of ox-serum cannot be recognised in the 

 foetal blood, even when a considerable quantity is injected. 3 The 

 reason appears to be that the proteins of ox-seruin resemble more 

 closely the normal serum proteins of the rabbit and are metabolised 

 by the trophoblast, while egg-albumen cannot be utilised, 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, 4 the foetal rabbit absorbs slightly more oxygen 

 and gives off slightly more carbonic acid per kilogram per hour than 

 the mother. Hence the intensity of the metabolic reactions is slightly 

 greater in foetal life. This is directly opposed to the views held by 

 Pfliiger on theoretical grounds, and by Cohnstein and Zuntz 5 from 

 their experimental results. The second result of Bohr's experiments 

 has been already mentioned, viz. that in that part of the metabolism 



1 Lochhead, " Oil the Transmission of Nitrogenous Compounds from Mother 

 to Foetus," Tram. Obstet. Soc. Edinburgh, vol. xxxiii., 1907-08. 



2 Ascoli, "Passiert Eiweissdie placentare Scheidewand?" Zeit.f.physiol. C/mm. t 

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

 (see reference, note '. 



3 Lochhead, loc. cit. 



4 Bohr, loc. cit. 



5 Cohnstein and Zuntz, " Untersuclmngen iiber das Blut, den Kreislauf und 

 die At mini g der Saugetierfotus," PJIilget's Arch., vol. xxxiv., 1884. 



