MUSCULAR TWITCHINGS 763 



In this case, obviously, water diffuses into the skin, which 

 previously had lost water. 



There may be electrolytes which act similarly to cane- 

 sugar, but I have not yet found them. Every solution of 

 an electrolyte causes, above a certain concentration, an 

 immediate withdrawal of the feet, and this withdrawal is 

 the more energetic the more concentrated the solution. 

 This differs from the behavior of sugar and urea, which 

 above a certain concentration have the opposite effect. 



The lowest concentration at which the solutions of various 

 electrolytes will cause a pithed frog to withdraw its feet 

 instantly or in from five to ten seconds, is about as follows : 



HC1, 5 f ff or less 



NaOH, ft or less CaCl 2 f 



. XT ' o > % or a little less 



AgNO 3 , ^ or less 



FeCl 3 , ^ or less 



HgCl 2 to 



AlCla, _ f 



g III/ IU 2 



It almost looks as if the coagulating effect of the kations 

 upon proteids was of some importance. The powerful effects 

 of Ag, Cd, and Hg interfere somewhat with the conclusion 

 that we are dealing with a pure valency effect, which otherwise 

 seems to make itself felt. If, instead of the chlorides, the nitrates 

 or sulphates of the same metals are chosen, the order of effi- 

 ciency seems to remain practically the same, as far as can be 

 judged from an as yet incomplete series of experiments. 



As far as the anions are concerned, the order of efficiency 

 is for the sodium salts about as follows: 



Na 2 oxalate f NaHCO 3 



Na 3 citrate, % Na formiate m 



Na 2 SO 4 , ? Na 2 succinate f 1 s 



NaHP0 4 ,f NaCl 



NaF, f to f 



