486 THE PHYSIOLOGY OF REPRODUCTION 



out by the ovum itself. There is no reason to believe that the 

 mammalian ovum, after acquiring the property of intra-uterine 

 development, has lost its metabolic activity. 1 



In addition, we possess positive evidence of metabolic 

 activity in the mammalian ovum. The results of Bohr's in- 

 vestigations on the respiratory exchange of the foetus (see p. 436) 

 mean nothing if they do not afford proof of this. As a large 

 amount of energy is generated, while, at the same time, practically 

 none is dissipated as heat evaporated or radiated from the surface 

 or lungs, the unavoidable conclusion is that the foetus itself 

 carries out the work of organisation, and utilises the energy for 

 its fulfilment. 



When we come to consider individual substances, we obtain 

 further evidence of activity, at least in the extra-embryonic 

 ectoderm or trophoblast. In no order of Mammals has the 

 transmission of haemoglobin as such from mother to foetus been 

 demonstrated. Even if it is absorbed as such by the tropho- 

 blast, it undergoes changes of such a nature that the iron- 

 containing part of the molecule is less firmly bound. In all 

 animals in which special investigations have been made, such 

 loose organic compounds of iron have been observed. In this 

 connection, reference may once more be made to Hofbauer's 

 statement that the histological appearances argue not only 

 for a decomposition of maternal haemoglobin in the syncytium, 

 but also for a synthesis of its derivatives into organic compounds 

 in which the iron is more firmly bound (see p. 480). 



The trophoblast probably acts also on simpler proteins. 

 If ox- serum is injected into a pregnant rabbit, its proteins 

 cannot be detected by the biological reaction in the serum of 

 the foetus. It may be that the trophoblast rejects them 

 altogether, but this is unlikely, since molecules of egg-albumen 

 are absorbed and transferred to the foetus (see p. 436). In all 

 probability the proteins of ox-serum are katabolised in the villi, 

 and, as a result, the constitution of the precipitable substance 

 is interfered with, and the precipitin reaction is negative. The 



1 If Hubrecht's view is correct, that the mammalian ovum is older than 

 the ovum of birds (see "Early Ontogenetic Phenomena in Mammals," Quar. 

 Jour. Micr. Sci., 1908), the sentence ought to read: "There is no reason to 

 believe that the fertilised ovum of birds acquired its metabolic activities only 

 after the loss of viviparity." 



