120 



O. F. HUTTER 



005 



30 

 Time C min') 



Fig. 4. Efflux of *'-Br from a frog's sinus venosus loaded in **'-Br-Ringer"s solution 

 for 1 hr. Abscissa, time from transfer into inactive Cl-Ringer"s solution. Left 

 ordinate, radioactivity in tissue or a logarithmic scale. Right ordinate, rate 

 coefficient for loss of ^sBr. Vertical bars give L s.e. During the first 20 min the 

 temperature of the inactive wash solution was C, thereafter 20 C. The loss of 

 isotope during the first i min of the experiment is not shown. From 29 to 35 min the 

 preparation was arrested by treatment with acetylcholine 5 • 10-" g/ml. The 

 specific activity of the Br-Ringer"s solution was lO"" counts/min equivalent to 

 10-7 X 10-^ mM Br. Tissue weight, lightly blotted, 2-7 mg. Total tissue K, 127 X 



10 -"^ mM. 



demarcation between the extracellular and cellular components. After 20 min 

 the preparation was returned to room temperature and it soon started to 

 beat regularly at 44/min. A period of treatment with acetylcholine was then 

 interposed. This causes the usual arrest but evidently had little effect on the 

 movement of bromide. Occasionally a transient or delayed increase in the 

 outflow rate was seen during the action of acetylcholine, but the changes were 

 too irregular and small to justify a positive interpretation of the experiments 

 as a whole. Attempts to test the action of acetylchoHne on the uptake of 

 bromide similarly failed to reveal a significant change. 



The experiments made with chloride all involved loading preparations in 

 solutions of high [Ko] X [Clo] product, in order to enrich the fibres with 

 chloride; in that sense they were less physiological and more difllicult to 

 interpret than the experiments with bromide. They gave opportunity, how- 



