ON THE MAMMALIAN NERVOUS SYSTEM. 325 



by the bulbo-spinal centres to the passage of the impulses, from the spinal cord out 

 into the nerve (see p. 458, Chapter X.). The further recent experiments of WEDENSKII* 

 seem to suggest that these waves in the muscular record may be to some extent 

 in relation with the block offered by the motor endings of the nerves in the muscles, 

 since he finds that such muscular intermittence may be produced by stimulation 

 of the nerve itself with rapid rates, an intermittence which, not being synchronous 

 with the rate of stimulation, but having its own rhythm, is presumably referable 

 to the neuro-muscular mechanism. 



As regards the after effect, the clonic stage, it is frequently separated from the 

 tonic stage by a distinct pause or interval ; this is of course visible in all methods of 

 exploration, to which the electrical investigation of the spinal cord is no exception. 

 When it occurs, therefore, it is obvious that after the cortex has been roused to 

 discharge, thus evoking the tonic stage, it possesses the power of again emitting 

 impulses when thrown into a high state of excitation. The period at which this 

 clonic discharge commences is variable, there being in some instances a pause or 

 period of delay, whilst in others the intermittent or clonic stage may even overlap 

 the tonic condition, which, consequently, ceases prematurely, while yet the excitation 

 is being continued. 



The clonic stage, or after effect, has a distinct rhythm (see graphic method, p. 273), 

 in which the muscles respond to intermittent impulses. Exactly the same is seen in 

 the electrical changes of the spinal cord. This stage, or after effect, as it truly is, 

 presents three chief features for study : (l) Its commencement ; (2) its development ; 

 (3) its mode of termination ; these being common to both the muscular and the spinal 

 records. 



(1.) The clonic stage invariably begins with small, often single discharges, vide fig. 6, 

 these soon increase in strength. This is of course closely imitated by the graphic 

 records of the muscle, the contractions of which, minimal at first, become, later, 

 maximal. 



(2.) The further development of the stage is marked by summation of the impulses, 

 the rhythm of which, directly measured, appears to be about 10 per sec., but we 

 have not yet had time to thoroughly investigate this point. ( Vide graphic method, 

 p. 273.) 



The summation of the electrical variations very obviously harmonises with all the 

 other facts relating to the persistence of the muscular contraction, when produced 

 by cortical stimulation. (See also FRANCOIS FRANCK and BUBNOFF and HEIDENHAIN, 

 loc. cit.) 



(3.) The termination of the series of intermittent variations is marked by their 

 becoming fewer, larger, and finally ceasing abruptly (vide fig. 6), very rarely 

 diminishing to final disappearance. 



* WEDENSKII, Archives do Physiologic Normalo et Pathol. (BEOWN-SfiQUARD), Jan., 1891. 



