220 Buchanan 



plate) was from 8-8 to 80 per second. In the next three, with the cord 

 cooled again, it was from (iG to 6'0 per second ; and in the last three, with 

 the cord warmed again, it was either 90 or S'O per second, and would have 

 been 9"0 in all three if the estimation had been made from the first three 

 waves only in the second response. 



It would appear, therefore, from these two sets of experiments, that in 

 the electrical responses of frog's muscle to a stinuilus which comes, in the 

 last instance, from the central nervous system, two kinds of rhythm may 

 manifest themselves in capillary electrometer records. The one of them, 

 that of the wavelets, which is very rarely absent in the responses of muscle 

 in strychnine spasm, gives us no positive information as to the nature of 

 the stimulus which immediately provokes the response ; but, from the con- 

 ditions under which the frequency may be modified and from those which 

 fail to modify it, we learn that the existence of a rhythm of this kind in 

 the response is no indication of the existence of a similar rhythm in the 

 stimulus, and since a single wavelet has a duration similar to that of a 

 response to an instantaneous stimulus, we may infer that the central 

 stimulus is not of the nature of a series of such stimuli. 



The other kind of rhythm, that of the waves, which is much more 

 frequently absent from the records, and the absence of which seems to 

 be determined b}^ the extent to which the animal is affected by the 

 drug at the time the records are taken (I say advisedly " the animal " 

 and not " the central nervous system "), does apparently, when present, 

 tell us the rate at which stimuli were coming from the cord at the time. 

 The form of each wave also tells us that the effect of each stimulus 

 was reduced, sometimes even to zero, before the effect of the next began, 

 and suggests (but this is by analogy only at present) that each stimulus 

 had a duration corresponding only to that part of the wave in which 

 wavelets are present. Moreover, the different forms of wave which 

 occur in different experiments suggest that this stimulus (" Zeitreiz " of v. 

 Kries) sometimes rises to its maximum strength quickly and sometimes 

 slowly. My records, in which waves are altogether absent, suggest, as did 

 V. Kries 's observations (7) and (8), that a single central stimulus may have 

 quite a long duration — not infrequently one of a third of a second — some- 

 times even lasting for a whole second [see (4), pi. ix., ph. 46]. It is, 

 therefore, by a study of what occurs in this 3 to 14 per second rhythm, 

 of what occasions its absence or presence, and of the conditions which 

 modify it, that we can alone hope, it seems to me, to come to any satis- 

 factory conclusions as to the natui-e of the normal stimulus, and to ascertain 

 whether or not it is rh^^thmical. For this purpose we must use animals 

 in which it is possible to modif}^ conditions for any one part independently 

 of other parts ; and, since temperature is the easiest condition to alter, it 

 ma}' be that polikothermal animals will give us most information. But the 

 experiments will have to be repeated with warm-blooded animals before we 

 are prepared, when we meet with a rhythm in the effect of so complicated a 



