142 



HODGE. [Vol. VII. 



showing the influence of sleep upon volitional power, must be 

 closely connected with, if not entirely dependent upon, events 

 taking place in the central nervous system. 



If any such rhythm exists in the cells of the spinal ganglia, 

 it is evident that such curves as we have drawn may be pro- 

 foundly influenced by it. A stimulation of five or ten hours is 

 physiologically a trivial matter compared with a fundamental 

 rhythm which has become through generations an established 

 fact in the economy of an animal species ; and if the changes 

 in such a rhythm are similar to those which have been demon- 

 strated by means of artificial stimulation, then clearly the effects 

 in each case have been resultants between the influence of 

 stimulation and the tendency of the animal's rhythm at the 

 time. That is, if stimulation be applied while the animal's 

 curve is falling most rapidly into sleep, we should not expect the 

 same effect which would be obtained were the animal's curve of 

 nervous activity on the rise. 



A young dog stimulated severely for ten hours, from 5.30 p.m. 

 until 3.30 A.M., showed scarcely a trace of fatigue. The purpose 

 of the experiment was by no means to illustrate the point under 

 discussion, but to obtain the greatest amount of change possible 

 in the spinal ganglion cells. The result, at the time, struck 

 consternation. Facts which it was hoped were of general appli- 

 cation, fitting equally well the activity of nerve cells, wherever 

 found, in the animal series from the highest to the lowest, must 

 now be given most absurd limitations. This and this is true 

 for the spinal ganglion cells of a frog or cat, but not for the 

 same cells of a dog, and may or may not be true for man or 

 any other animal. The shock of this unexpected result was 

 paralyzing at first ; and whether we are justified in saying that 

 the tendency toward recovery, the tendency to sleep, in the 

 cells of the spinal ganglia was strong enough to counterbalance 

 an intense stimulus, which was sufficient to cause constant 

 and vigorous contractions of the muscles supplied by the 

 stimulated nerve, is doubtful, and plainly requires further 

 experiment to decide. This seems to be, however, the simplest 

 explanation of the phenomenon at present. And in saying 

 this, the writer is fully aware that, more than two hundred 

 years ago, Swammerdam studied reflex action in sleeping ani- 

 mals and men, and hence that the cells of the reflex arc must 



