MuscuLarR 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: 
HCl, am, or less MgCl, 
NaOH, #3 or less CaCl, ( ; 
AEN, B.vor'less SrCl, ™ or a little less 
FeCl;, 2% or less BaCl, 
CdCl, t ors KCl, ™ to 
HgCl, § #2 O18 NH.Cl, ™ to 3m 
AlCl;, %to® NaCl * a 
Tier § Sees 
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 
seemstomakeitself felt. If,instead of thechlorides, thenitrates 
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, oxalate ” NaHCO; 
Na; citrate, ” Na formiate tn toe 
Na.SOu., ” Na, succinate ( ° 
NaHPO,, 2 NaCl 
NaF, ? to ? 
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