42 K Uptake by Tissues in Pregnant Animals 149 



stages of pregnancy in rats and guinea pigs. A series of goats, 

 pregnant between 35 and 142 days, were subsequently used 

 for further experiments and the relevant results, together with 

 those on the rodents, are given below. The collection of 

 material from a series of goats allowed histological and histo- 

 chemical observations to be made on the changes occurring 

 in the placenta during the advancement of pregnancy. 

 These observations are briefly summarized below. 



Materials and methods 



Female albino rats weighing between 170 and 290 g. were 

 used; the animals were killed at times varying from the 11th 

 day of pregnancy until term. Female goats, mainly of the 

 British Saanen breed, were used; the goats were mated at 

 known times and were killed at intervals from the 35th day 

 until just before term. The portions of the uteri and placenta 

 not used for the estimation of radioactivity were fixed in 

 various fluids for subsequent histological and histochemical 

 examination by a variety of methods. 



Irradiated "Specpure" K 2 C0 3 was converted into an 

 aqueous solution (2 per cent or 0-2 per cent w/v) of 42 KC1, as 

 indicated by D'Silva and Neil (1951). In rats the amount of 

 K ion injected in each experiment was 0-3 to 1 -2 mg., and in 

 goats 60 to 90 mg., an amount insufficient materially to alter 

 the total amount of K in the extracellular fluid. Descriptions 

 of the technical procedures carried out in order to estimate the 

 radioactivity of the tissues will be found in the paper by 

 D'Silva and Harrison (1953). The potassium content was 

 determined by means of a direct reading flame photometer. 



Experimental results 



In a series of rats pregnant for 11 to 18 days the distribution 

 of 42 K in the uterus, placenta, kidney and foetuses was 

 studied 5 minutes after intravenous injection of 42 KC1. It will 



