752 STUDIES IN GENEKAL PHYSIOLOGY 



of the poisonous effects of Zn. In stronger solutions than 

 ^ no beats occurred. The same was true for ZnSO 4 . 

 Solutions of CdCl 2 and Pb(No 3 ) 2 also gave rise to a few 

 contractions in the concentration of about ^ to T ^. 



The fact that the more concentrated solutions of the salts 

 of heavy metals did not act is probably due to their poison- 

 ous effect. It is, therefore, evident that there are a number 

 of chlorides with bivalent kations which are able to produce 

 rhythmical contractions at a lower concentration than NaCl. 

 It would, therefore, be wrong to ascribe the inhibiting effect 

 of Ca salts upon rhythmical contractions to the double 

 valency and the positive charge of the Ca ions. 



3. Does the effectiveness of salts for the production of 

 rhythmical muscular contractions increase with the valency 

 of the anion? This is decidedly not the case, as the fol- 

 lowing table shows. In this table are given the minimal 

 concentrations of the solutions of various sodium salts in 

 which rhythmical contractions occur: 



Salt Minimal Effective 



Concentration 



NaCl {| 



NaBr ft 



NaJ 



Na acetate 



Univalent anions -< 



^Na formiate ^ 



f Na 2 succinate ft 



Bivalent anions -i ^HPO S m 



[Na 2 oxalate ^ 



Trivalent anions \ XT 



It is obvious that the power of favoring rhythmical con- 

 tractions in muscles is not an unequivocal function of the 

 valency of the anion. It is likewise obvious that the sodium 

 salts whose anions precipitate calcium powerfully, like sodium 

 fluorides, sodium oxalate, and sodium phosphate, are among 



