May 8, 1903.] 



SCIENCE. 



729 



investments must be safe and the net in- 

 come large. It is believed that no guardian 

 would more surely fulfill these conditions 

 than the corporation of Harvard College. 

 Edward C. Pickering. 

 Cambridge, Mass., 



April, 1903. 



THE NATURE OF NER.VE IRRITABILITY, 

 AND OF CHEMICAL AND ELECTRICAL 



STIMULATION. PART II. 

 The present paper contains results con- 

 firming and extending those given in my 

 paper in Science, Vol. XV., pp. 492-498, 

 1902. The results previously reported 

 were interpreted to mean that chemical 

 stimulation by salts, apart from the osmotic 

 stimulation of strong solutions, was really 

 an electrical stimulation due to the electric 

 charges of the dissociated ions. Of these 

 ions the negative or anion always tended 

 to stimulate the nerve, while the positive 

 or cathion always tended to reduce nerve 

 irritability and prevent stimulation. 

 "Whether any salt stimulated or annihilated 

 nerve irritability without stimulation de- 

 pended upon the predominance of the anion 

 or the cathion. Chemical stimulation was 

 shown to be in reality electrical, instead of 

 electrical stimulation being chemical as had 

 hitherto been supposed. These results 

 made it possible to understand electro- 

 tonus and electrical stimulation. The 

 cathode increases nerve irritability and 

 stimulates, because in this region anions 

 are predominant during the passage of the 

 current; while the anode depresses because 

 here the cathions preponderate. Stimula- 

 tion on the break of the current was due 

 to the reverse of these processes, the ac- 

 cumulated anions diffusing toward the 

 cathions, and a fall in the positivity of the 

 nerve in the anode region resulting. Fur- 

 thermore, the specific action of the ions 

 upon the nerve was supposed to be due to 

 a production of a change in state in the 



colloids in the nerve, extending Loeb's 

 hypothesis in this particular and making it 

 specific that stimulation meant a precipita- 

 tion of the colloids, inhibition the reverse; 

 the colloids of the motor nerve reacting as 

 if they were electro-positive. 



Since the publication of this paper, ill- 

 ness and the pressure of other work have 

 prevented my bringing the matter to a 

 conclusion as soon as I had hoped, and 

 meantime Loeb has published an attack on 

 my hypothesis so far as it applies to 

 muscle.* 



Loeb has been led to abandon this hy- 

 pothesis because of certain exceptions, 

 among them being the action of barium 

 chloride. Further work, of which the fol- 

 lowing is a preliminary statement, estab- 

 lishes, I believe, the truth of the main con- 

 clusions in my former paper, so far at 

 least as motor nerves are concerned. In 

 the case of the muscle I can not but think, 

 from Loeb's results, that a careful study 

 of apparent exceptions might show the 

 same facts there, and explain these excep- 

 tions, as has been the case with the nerve. 

 As regards the possibility of sensory 

 nerves showing a different reaction to 

 motor, Griitzner long ago pointed out the 

 fact that they were readily stimulated by 

 potassium chloride and acids, while motor 

 nerves were not. Every one knows that 

 acids will stimulate some sensory end or- 

 gans, presumably by means of the positive 

 ions the acids contain. Knowing these 

 facts, it was easy to infer that sensory 

 nerves were electro-negative and were stim- 

 ulated by salts having a predominant posi- 

 tive ion, while motor nerves were electro- 

 positive and were stimulated by the anion. 

 Were this true, we should have a posi- 

 tive variation in sensory nerves and a re- 

 verse electrotonic effect from that in motor. 



* Loeb, Pfliigers Arohiv f. die ges. Physiologie, 

 Bd. 95, 1902, p. 255. 



