Biochemical Evidence of Ageing in the Placenta 143 



production of lactate and C0 2 , and in initial glycogen and 

 water content, these placentas did not differ significantly from 

 normal placentas of a comparable age. These results confirm 

 and extend those of Heilman, Harris and Andrews (1950). 



The data presented make it clear that the decreases in 

 metabolic rate are not uniform. Some functions decrease 

 more rapidly, and begin at an earlier time, than others. 

 Glycogen synthesis appears to be one of the first to decrease 

 markedly. 



The term placenta, as judged by its metabolic activities in 

 vitro, is still quite active. It would seem inaccurate to speak 

 of it as "senile". There is, furthermore, no sharp change at 

 term which could be used to explain the initiation of labour. 

 One could postulate, perhaps, that labour is induced when 

 some critical ratio between the demands of the child for 

 nutrients and the ability of the placenta to supply them is 

 exceeded. The change in the ratio would be brought about, 

 however, more by the rapid increase in the demands of the 

 child as its mass increases than by the decrease in the ability 

 of the placenta to supply nutrients. 



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