178 
Proceedings of Royal Society of Edinburgh. 
[sess. 
author has shown to occur, the recording apparatus must a priori he 
kept in oscillation at its own period, just as a swing will he kept 
swinging when even occasional pushes are given, The complete 1 
demonstration of this truth is obtained by changing the record- 
ing apparatus, when not only will the oscillations he changed, 
but they will he found to correspond with the period of the in- 
strument used in every case. This period can be obtained by 
tapping the instrument, and causing it to record its own oscilla- 
tions. Loven has obtained variations in the electromotive force 
of a muscle during voluntary contraction ; these variations are 
described as periodic, and are believed to support the view held as 
to the interrupted nature of the nerve impulses passing to a muscle. 
His results differ from those of other observers in respect to the 
period of his variations, and probably his results are due to the 
period of the electrometer he used. 
If then the muscle sound, the results obtained by Loven, and the 
tracings obtained by the use of levers, can all he explained by the 
fact that the fasciculi within a muscle are not completely co-ordinated, 
there remains no proof that a voluntary muscular contraction is of 
the nature of a tetanus. 
Muscular Contraction following rapid Electrical Stimula- 
tion of Central Nervous System. By John Berry 
Haycraft, M.D., D.Sc. 
{From the Physiological Laboratory of the University of Edinburgh . ) 
(Read February 28, 1890.) 
{Abstract.) 
Kronecker, Hall, Schafer, Horsley, and others have found, when 
stimulating the spinal cord with rapid induced currents (ten, twenty, 
thirty, forty times per second), that the muscles always responded 
by giving a curve showing oscillations of one invariable period, no 
matter what the period of the stimulation may have been. With 
rapid stimulation, the muscles in the hands of the first named 
observers gave oscillations of twenty a second, in the hands of the 
latter observers of ten a second. These results are to be explained 
in the following way. When the central nervous system is stimu- 
