604 LAWRENCE W. COLE 



in each of the four solutions. Ordinarily five records were ob- 

 tained from each for each salt, though occasionally a frog ceased 

 to react before the required twenty records were completed. 

 Each frog was given two minutes in which to respond. A failure 

 to react within that time was called " no reaction ' ' and is indicated 

 by the letters N.R. in the tables. The experiments were begun 

 early in April and as the season advanced the frogs gained in 

 activity, so that more than twenty records were readily obtain- 

 able in experiments made in the latter part of April, in May, and 

 in early June. But when the weather became warm in June, 

 it was found that the frogs again succumbed quickly to the effects 

 of the operation. Experiments in very warm weather were, 

 therefore, not feasible. 



In examining table 1, it will be seen that ammonium chloride 

 and potassium chloride are almost balanced in effect so far as the 

 four frogs are concerned, for with frogs B and C ammonium pro- 

 duced a reaction more quickly than potassium, while with frogs 

 A and D, potassium caused the quicker response. When, however, 

 the general averages, from these solutions are compared, ammo- 

 nium chloride (2.03 seconds and 2 "no reactions") is seen to call 

 forth a slightly quicker reaction than potassium chloride (2.14 + 

 seconds and 2 "no reactions"). Next to potassium chloride in 

 quickness of the reaction called forth from all four frogs is sodium 

 chloride with a general average of 2.84 seconds and 3 "no reac- 

 tions," while lithium chloride, which has a general average of 

 3.82+ seconds and 3 "no reactions," is slowest. Thus 3 m. solu- 

 tions of these four salts are not equally stimulating, but they 

 form a series, which, passing from the most stimulating to the 

 least, is ammonium, potassium, sodium, and lithium. 



It will be seen from table 2 that at a concentration of 2 m. am- 

 monium chloride again calls forth the quickest reaction, the aver- 

 age time being 3.64 seconds. As at concentration 3 m., ammo- 

 nium is here followed in sequence by potassium (4.34 seconds), 

 sodium (15.54 seconds), and lithium (18.86 seconds + 1 N.R.). 

 Moreover, at a concentration of 2 m. the four salts are clearly 

 divided by their reaction-times into two groups — ammonium 

 and potassium: sodium and lithium — a condition suggested in 



