612 LAWRENCE W. COLE 



it to be in stimulation by acids. He proposes as an explanation 

 of stimulation by salts that the osmotic pressure may act as a 

 stimulus and therefore that the summation of stimuli is an impor- 

 tant factor in the reaction-time. Consequently he believes that 

 the action of salts maybe regarded as (in a sense at least) a mechan- 

 ical stimulation. This view, that both the diffusion-time and 

 summation-time are parts of the total reaction-time, would lead 

 us not to expect a proportional relation between the reaction- 

 time and the degree of dissociation of the salt. 



Braeuning's view seems to receive support from my observa- 

 tions on frogs with an abraded foot, but on the other hand the 

 fact, as will be shown presently, that cocaine interferes so little 

 with these reactions, must be taken into consideration in deter- 

 mining the nature of the stimulus. 



In concluding the comparison of reaction-times and degrees of 

 dissociation, it may be said that, though there is a fairly close 

 relation between these two factors, this relation is probably not 

 as close as may be implied in some of the tables. Thus, at 3 m.- 

 and 2 m.- concentration the ammonium salts are slightly more 

 dissociated than the potassium salts, while at 1 m. the reverse is 

 true and the reaction-times indicate a like relation. It is, how- 

 ever, improbable that the frogs react to these slight differences, 

 and I believe this feature of the tables to be accidental. 



It seems quite probable that the time required for diffusion is 

 in a strict relation to the degree of dissociation and that this 

 relation is slightly disturbed by the added factor of summation of 

 stimuli, or nervous reaction-time. 



Since chlorine is the common ion in these salt solutions and yet 

 the results maintain a uniform series of differences in different 

 solutions, the chlorine would seem to have either no effect upon the 

 frogs or a uniform effect in such series of solutions of the same con- 

 centration. The differences in reaction must, therefore, be due to 

 the effects of ammonium, potassium, sodium, and lithium ions. 

 Kahlenberg ('98) in writingof the effects of these ions on t hesense 

 of taste, says that, "lithium ions have no pronounced taste, their 

 effect is somewhat like that of sodium, though less in degree. 

 Potassium ions have a more pronounced taste than sodium ions, 

 and ammonium ions also have a bitter taste." 



