42 K Uptake by Tissues in Pregnant Animals 151 



rate of blood-flow through the uterine vessels (Barcroft and 

 Rothschild, 1932; Barcroft, Herkel and Hill, 1933) together 

 with a rapid rate of exchange of K ions. 



A further series of experiments was carried out on goats 

 of various breeds, pregnant from 35 to 142 days, into which 

 radioactive 42 KC1 was injected 15 minutes before death. In 

 almost every animal portions of the kidney and liver were 

 removed and the radioactivity determined. In all but two 

 animals the activity of the plasma was also determined and 

 this allowed calculation of the relative potassium activity 

 (R.P.A.). The latter is calculated according to the following 

 expression : 



Activity of tissue mg.K/g. of plasma 

 ~ Activity of plasma mg.K/g. of tissue 



where the activity is defined by the expression given in the 

 footnote to Table I. 



Table II shows that the radioactivity of both the kidney 

 and liver varied widely in different animals, but there was no 

 systematic change in relation to the duration of pregnancy. 

 On the whole, the radioactivity of the tissue was directly 

 related to its potassium content which is shown by the rela- 

 tively small variation in the figures for the R.P.A. of kidney 

 (column 7) and of liver (column 10). 



The membranous chorion was removed from portions of the 

 uterine wall and areas of mucosa carefully stripped from the 

 underlying muscle. The radioactivity and K content of the 

 uterine muscle and mucosa are shown in Table III. There 

 were large changes in the radioactivity of these tissues in 

 different experiments but these were roughly paralleled by 

 changes in K content. Therefore the R.P.A. values for uterine 

 muscle (column 5) and mucosa (column 8) were much less 

 variable than either the radioactivity or the K content. 



In each animal either a whole placentome, or a portion of 

 one, was removed and examined for its activity and its 

 potassium content. In several animals a number of placen- 

 tomes of varying shape and size were examined individually ; 



