POTASSIUM IX YEAST CELLS 



919 



in the cyclotron. The radiof)o(iissium used in our experiments had an activity 

 amounting to less than 0.001 milliCuric. This activity was found not to influence 

 the growth of the yeast. 



Radioactive Analysis 



By comparing the radioactivity of the yeust and the nutrient solution .samples 

 we obtain the ratio of their ^^K content^i^ The comparison was carried out by 

 using a Geiger counter. As the weight of the yeast samples was much smaller 

 than the weight of the nutrient solution samples, we mixed some ash non-active 

 nutrient solution to the yeast samples and obtained thus yeast samples having 

 the same weight and almost the same composition as the active nutrient solution 

 samples. The ash sample obtained by this procedure weighed about 120 mgm. 

 It was put in a small aluminium dish of 1.1 cm diameter and placed under the 

 window of the Geiger counter. The procedure described above has the advantage 

 that the absorption of the radioactive (^) radiation in the samplers, the activity 

 of which is to be compared, becomes equal and thus can be disregarded. 



RESULTS 



In some experiments (I, II, and III), labelled yeast was suspended in 

 non-labelled nutrient solution and by analysing the samples taken at 

 intervals the amount of ^'^K was determined which migrated from the 

 yeast into the nutrient solution. The labelled yeast was obtained by 

 growing yeast in a nutrient solution containing labelled potassium. 



In other experiments (IV and V), non-labelled yeast was placed in 

 nutrient solution containing labelled potassium. At different intervals, 

 samples of yeast and nutrient solution were taken and their ^H\. and 

 their total potassium contents were determined. 



Table 1. — Analytical Data 

 (a) Yeast placed in nutrition solution containing *^K 



''' The "natural" radioactivity of potassium could be neglected in our experiments. 



