764 STUDIES IN GENERAL PHYSIOLOGY 



In this case, as in the case of rhythmical contractions, 

 the oxalates and citrates are the most powerful anions of 

 this series. It is clear that, in the determination of the 

 lowest concentration of a salt which is still able to cause the 

 immediate withdrawal of the foot, one must remember that 

 a number of solutions (e. g., AgNO 3 , A1C1 3 , FeCl 3 , HC1, 

 NaOH, Na 3 citrate, etc.) have an after-effect which makes 

 itself felt in an increase of irritability. Other solutions 

 (e. g., those of calcium salts) may possibly have the opposite 

 effect, namely, to raise the threshold of stimulation for sub- 

 sequent tests. 



It was of some interest to ascertain whether the results in 

 these experiments were produced through an action of the 

 electrolytes upon the nerve-endings, or upon the nerves 

 themselves. In experiments upon frogs whose skin had been 

 removed from the feet, the results described in this paper 

 could not be produced. The experiment of putting the nerves 

 themselves into the above-mentioned solutions remained prac- 

 tically without effect. It is possible that with solutions of 

 much greater concentration results may be obtained. It is, 

 therefore, certain that the results observed in our experiments 

 are due to an action of the electrolytes upon the nerve-endings 

 in the skin, and not to an action upon the sensory nerves. 1 



IV. CONCLUSIONS 



The experiments mentioned in this paper were undertaken 

 with two aims in view, a practical and a theoretical one. As 

 far as the former is concerned, it follows from our investiga- 

 tions that abnormal muscular twitchings and contractions 

 may be brought about in an organism by a reduction in the 

 proportion of calcium (or magnesium) in the muscles or the 

 blood, or an increase in the proportion of Na and other 



iThe chemical irritability of muscles is, as far as electrolytes are concerned, 

 also greater than that of motor nerves. The reverse is true for electrical stimula- 

 tion. 



