752 STUDIES IN GENERAL PHYSIOLOGY 
of the poisonous effects of Zn. In stronger solutions than 
#z no beats occurred. The same was true for ZnSO,. 
Solutions of CdCl, and Pb(No,), also gave rise to a few 
contractions in the concentration of about 5%, to 7%. 
The fact that the more concentrated solutions of the salts 
of heavy metals did not act is probably due to their poison- 
ous effect. Itis, 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 m 
| NaBr mm 
Univalont anions 3 0 ge 
Na acetate mB 
a io 
Na formiate wm = ity 
m 
( Naz succinate 
i 
| 
* ¥ ! Na, sO, 5 
Bivalent anions NaHCO, m -# 
Na, oxalate 2eo — 500 
; : Na,HPO, Oe at 
Trivalent anions Ne. cities = eee 
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 
Digitized by Microsoft® 
