602 LAWRENCE W. COLE 



ployed on frogs by Loeb ('02), and by Braeuning ('04). After 

 suspension both hind feet of the frog were dipped into a given 

 solution up to the ankle, care being taken to avoid contact with 

 the sides of the containing vessel. A frog whose feet were thus 

 dipped would withdraw them after they had been in the solution 

 a few seconds, and this period, while variable, is significant for 

 the particular solution. These periods usually became longer 

 as the trials proceeded, a condition due probably more to the 

 gradual death of the animal's tissues than to the direct effects of 

 the salts. 



A frog dipped in this way in ordinary tap-water or distilled 

 water did not withdraw the feet at all. The time from the mo- 

 ment of immersion to the moment of withdrawal was taken in 

 seconds and fifths of a second by means of a stop-watch. This 

 time, which may be called the reaction-time, 1 is much shortened 

 when there is an abrasion of the skin on the frog's foot. In such 

 cases the animal responds quickly with the abraded foot antl often 

 much more slowly with the uninjured one. Fatigue effects were 

 eliminated by returning each frog to a vessel of water during the 

 time required to test three others, and as the four salts were tried 

 in a different sequence in each one of every series of four animals, 

 the order of procedure could have no effect on the averages of the 

 reaction-times. For example, in table 1, the first frog (A) was 

 dipped successively in potassium, sodium, ammonium, and lith- 

 ium; the second (B) in sodium, ammonium, lithium, and potas- 

 sium; the third (C) in ammonium, lithium, potassium, and 

 sodium and so on. Hence the average reaction-time for any one 

 salt cannot have been influenced by the position of that salt in 

 the series of tests. The experiments wore made at a uniform 

 room temperature. 



The reaction-times were recorded as in table 1; each number 

 here being the record of one trial and each frog in order being tried 



1 From the behavior of fro^.s with abrasions of the skin, I believe that the reac- 

 tion-time proper is but a small part of the total time which elapses between im- 

 mersion and withdrawal. The major part of this time seems to be that required 

 for the solution to pass far enough through the skin to meet the nerve-endings. 

 The skin seems to present a considerable obstacle to t his passage. 



