494 



SCIENCE. 



[N. S. Vol. XV. No. 378. 



My observations were made on the sciatic 

 nerve of the frog and stimulation of the 

 nerve was shown by the contractions of the 

 gastrocnemius miiscle. I have tried aboi;t 

 nine hundred experiments on frogs at dif- 

 ferent seasons of the year, so that the 

 observations are numerous enough to offset 

 most individual variations. The nerves 

 were immersed for the greater part of their 

 length in the solutions to be tested. 



1. Nerves are stimulated by the with- 

 drawal of water. The non-electrolytes 

 sugar, urea and glycerine will stimulate if 

 the osmotic pressure of their solutions is 

 equal to, or greater than, twelve atmos- 

 pheres. This is more than twice the osmotic 

 pressure of the nerve. Nearly all electro- 

 lytes tested, qviite irrespective of their 

 nature, will also stimulate if their solutions 

 are as concentrated as this. The nerve 

 always increases in irritability (katelectro- 

 tonus) before impulses large enough to 

 cause the muscle to contract are generated. 

 After complete loss of irritability in the 

 non-electrolytes the nerves will be com- 

 pletely restored by placing them in M/8 

 sodium chloride solution. These facts 

 demonstrate anew the truth of the gener- 

 ally accepted opinion of physiologists that 

 the change in the nerve which generates 

 the nerve impulse can be set up by the 

 withdrawal of water. 



2. All salts of li, Li, K and NH^ which 

 were tested of which the anions are mono- 

 valent, such as KCl, KBr, KI, LiCl, NH.Cl, 

 and others; all salts of bivalent kations 

 united to monovalent or bivalent anions, 

 such as MgCL, MgSO,, MgCNOa)^, ZnCL, 

 ZnSO,, BaCL, BaCNOj),, CuSO,, SrCL; 

 all salts of trivalent kations united to 

 monovalent anions, such as Fe^Clo and 

 ALClg will generally stimulate if their 

 'solutions have an osmotic pressure of 

 twelve atmospheres or over. In solutions 

 weaker than this they all annihilate nerve 

 irritability without stimulation, H, K and 



Pcg salts most rapidly. Irritability may 

 generally be restored, if the nerves are not 

 left too long in the solutions, by immersion 

 in M/8 NaCl solutions. All these salts, 

 therefore, stimulate by withdrawing water. 

 The salts themselves will in each case de- 

 stroy irritability. 



3. All acids tested with the exceptions 

 (possibly) of phosphoric and oxalic will 

 not stimulate, except in solutions of high 

 osmotic pressure (twelve atmospheres) 

 Hydrogen ions do not appear hence to stim- 

 ulate the nerve. On the contrary in 

 weaker solutions tested, nerve irritability 

 was lost without stimulation. This con- 

 firms Griitzner and others. My experi- 

 ments, however, are not complete on this 

 point. 



4. Alkalies such as NaOH, LiOH, KOH, 

 Ba(0H)2 will stimulate in approximately 

 N/20 solutions. The hydroxyl ion, in other 

 words, at certain concentrations stimulates 

 the nerve. 



5. If we compare the stimulating action 

 of NaCl, NaBr, and Nal we find that these 

 salts stimulate even in solutions of the 

 same osmotic pressure as the nerve. The 

 stimulating action of the salts increases as 

 we pass from the chloride to the iodide. 

 Hence stimulation is in some way a func- 

 tion of the anion, because the rate of dif- 

 fusion of these salts is approximately the 

 same and the number of Na ions is con- 

 stant. It is not a function of the atomic 

 weight, since the fluoride stimulates more 

 than the chloride or iodide. These observa- 

 tions confirining Griitzner led to the con- 

 clusion that the stimulating action of salts 

 is due to their anions. On comparing the 

 action of NaoSO^, NajCaO^, NajHAsO^ and 

 other bivalent anion salts we find that these 

 are more powerful than the monovalent 

 anions; and the trivalent anion salts such 

 as sodium ferricyanide, sodium citrate and 

 NaaPO^ are still more powerful than the 

 bivalent anion salts. Thus NaCl and NaBr 



