730 



SCIENCE. 



[N. S. Vol. XVII. No. 436 



I accordingly tried experiments on the sen- 

 sory nerve trunks of frogs' more than a 

 year ago, but I found the response to 

 sensory stimuli so uncertain as to make the 

 results valueless. Further experiments 

 are necessary before speaking definitely, 

 but thus far I have been unable to obtain 

 any conclusively different results in sen- 

 sory from motor nerves. I mention this 

 fact to show that the argument that posi- 

 tive ions stimulate sensory end organs is 

 not incompatible with my own conclusions 

 and the facts were well knoAyn to me. 



1. The anion stimulates motor nerves; 

 the cathion reduces irritability. Loeb con- 

 tradicts this statement for muscle because 

 barium chloride stimulates muscle. The 

 stimulating action he refers to the cathion. 

 Barium chloride of an M/10 or weaker 

 solution will also stimulate motor nerves, 

 and is in these strengths a better stimulus 

 than an equivalent sodium chloride solu- 

 tion. My former statement including 

 barium chloride among the non-stimulants 

 was wrong, the mistake arising from a 

 series of negative observations. Mr. 0. 

 H. Brown called my attention to this 

 error. The stimulating action of barium 

 chloride is, however, due to the anion 

 and not to the barium, although barium 

 nitrate and acetate will also stimulate. 

 That it is the chlorine and not the ba- 

 rium which stimulates may be shown by 

 stimulating the nerve or the muscle with 

 non-polarizable mercury, calomel, barium 

 chloride electrodes. If barium stimulates 

 the contraction should begin at the posi- 

 tive electrode on the make of the current, 

 as well as at the negative, for at the anode 

 barium ions are passing into the nerve. It 

 was found that the contraction always be- 

 gan at the cathode on the make as with 

 sodium chloride. The experiment was also 

 tried of soaking the nerve or muscle in 

 barium chloride for many minutes previ- 



ous to stimulation, so that barium chloride 

 might be present in the muscle and nerve 

 in large amounts. No change in the na- 

 ture of the response could be observed. 

 Similar experiments with electrodes of 

 aluminum chloride, manganese chloride, 

 magnesium chloride, zinc chloride and 

 other metals gave the same results as 

 sodium chloride, except that a greater de- 

 pression may occur at the anode. These 

 facts show that the stimulation is due to 

 the anion and not to the cathion.* Fur- 

 ther evidence will be given to support this 

 conclusion. Barium chloride resembles 

 sodium chloride in many of its reactions, 

 so that there is little doubt that if the 

 sodium salts stimulate by their anions the 

 barium salts do also. I think it probable 

 that barium chloride stimulates because 

 the two charges on the chlorine overbal- 

 ance the two charges on the barium. This 

 physiological difference between barium 

 and calcium and sodium and potassium is 

 in line with their chemical behavior. 

 Barium chloride solutions contain no 

 hydrogen ions produced by electrolytic dis- 

 sociation, while calcium and magnesium do ; 

 and potassium chloride, while not contain- 

 ing hydrogen ions itself, facilitates catal- 

 yses produced by such ions, while sodium 

 has not this property. Why the two cal- 

 cium charges are more efficient than the 

 two barium charges is still obscure, but 

 may be due to the charge being more firmly 

 attached to the barium than to the calcium, 

 or that the charge has a different motion 

 in the two cases. 



2. The relative stimulating efficiency of 

 the anions is primarily, as already stated, 

 proportional to the number of charges on 

 the anions. Further observations on more 

 nerves and other salts show that the mono- 

 valent anions are to the divalent and the 



* I owe the suggestion of using electrodes in this 

 way to Dr. Lingle, who has already employed it 

 on heart muscle. 



