148 F. H. SCOTT. 



publications. Samples of the various types may be seen in the 

 figures. There is usually a tetanic contraction (Figs. 1, 2, 3, 4), but 

 occasionally the contraction is little more than a simple twitch (Fig. 7). 

 Sometimes the prolonged tetanic contraction tends to become alterna- 

 tions of contraction and relaxation, but not always, and often the 

 responses are alternating from the beginning (Fig. 2). 



The movement obtained at first usually lasts about a minute, and 

 then the muscles gradually return to rest although the stimulation is 

 continued. After a short pause in the stimulation a second but shorter 

 movement may be obtained. These alternate periods of stimulation and 

 rest may be repeated a certain number of times, and a long time elapses 

 before the last trace of movement disappears. Finally, however, even 

 after long periods of rest no response can be obtained. In most cases 

 the roots were stimulated for given periods, usually 30 seconds and then 

 30 seconds rest allowed. When the root failed to give a response after 

 the 30 seconds rest, a longer pause ( to 2 hours) was allowed. After 5 

 or 6 of these periods of stimulation the responses (after a long rest) in a 

 period of stimulation became less and less, and finally no more response 

 could be obtained from it as long as the frog lived (compare upper 

 tracings of Figs. 2, 3, 4, 5, and 6, 7, 8). This condition of ineffectiveness 

 of the root was true, not only for the weak current which had been 

 used for the excitation, but also for the strongest currents which could 

 be applied. There is, of course, great difference in the total duration of 

 movement obtainable from such a severed dorsal root. Ordinarily one 

 can obtain 15-40 minutes' movement (in all), after which no further 

 response can be evoked, however long the frog be kept (2-3 days). A 

 few frogs gave a greater total response than 40 minutes, and quite a 

 number a smaller one than 15 minutes. The smallest total for a cut 

 root equalling 4| min-utes, and the largest 69 minutes. In three cases 

 the root was not exhausted as rapidly as possible but only a few periods 

 of stimulations given per diem. The totals in these experiments extend- 

 ing over 4 days were 18, 24 and 40 minutes. These numbers were 

 often exceeded in less time, as the table (I) shows, and indeed as much 

 as 37f minutes was observed during the first 3 hours of one experiment 

 (No. 4, Table II). 



During the time of these experiments the root left as a control loses 

 none or very little of its power to keep the muscles contracted. Table I 

 shows the results of some of these experiments. Many more were made, 

 at first to ascertain the truth of foregoing statements, but as in these 

 earlier experiments the total duration of movement obtained was not 



