150 



R. J. Harrison and J. L. D'Silva 



be seen from Table I that with the smallest foetus (<9 mm.) 

 the radioactivity in the uterus was less than that in the 

 placenta. When the foetus was 9-18 mm. long the reverse 

 was true. The results of a larger number of experiments, 

 carried out near term and involving the sacrifice of the animals 



Table I 



The Activity of Tissues in the Pregnant Rat 5 Minutes 



after Intravenous Injection of 42 KC1 



* Includes foetal fluids. 



Activity of uterus, placenta and foetuses at various times after injection of 42 KC1 into rat9. 

 Results are expressed as percentage (x) of total radioactivity, x is defined by the expression : 



_ counts/min./g. tissue 



— total injected counts/min. 

 where D is a correction factor allowing for decay. 



x 100 D 



at intervals of 5 minutes to 24 hours after injection of 42 KC1 

 are described in the paper by D'Silva and Harrison (1953). 

 The activity of the labyrinthine placenta near term falls from 

 • 53 per cent (per g. of tissue) of the total radioactivity after 

 5 minutes to • 29 per cent after 24 hours. It is suggested that 

 these results could be explained on the assumption of a slow 



