LASHLEY— CEREBRAL FUNCTION 273 



areas, either at cortical or subcortical levels, since stimulation of the 

 precentral gyrus renders the otherwise inexcitable postcentral gyrus 

 excitable for corresponding movements. 



After partial recovery from cerebral paralysis, the most prominent 

 symptom is the weakness of the formerly paralyzed limbs. The greater 

 part of their repertoire of movements may be restored, speed may be 

 nearly normal, but only a slight force can be exerted, and fatigue occurs 

 readily. What is lacking in this condition is not an adequate integra- 

 tion of the motor impulses, but a sufficient mass of neural impulses to 

 maintain muscular activity. This may be ascribed either to a reduction 

 in the number of functional nerve cells, or to inadequate facilitation. 

 The ready fatigability is evidence for the latter. 54 



There is evidence that the withdrawal of facilitation derived from 

 other sources will produce similar weakness and fatigability and a ten- 

 dency not to use the affected parts. Thus Munk 55 has shown that 

 denervation of a limb has such effects, and Sherrington's 50 work has 

 demonstrated that they are due to the withdrawal of impulses derived 

 largely from the denervated muscles. 



The importance of such facilitating systems has been emphasized 

 by a number of recent investigators (Monakow, 57 Wilson, 42 Sherring- 

 ton, 58 Tournay, 59 Hunt 00 ). The general conception of these investi- 

 gators is of a series of hierarchies of motor reflexes, all exerting a 

 facilitating influence on the final common path. These involve at least 

 the following elements. 



54. The all or nothing principle of nerve and muscle activity requires the 

 assumption that strength of muscular contraction is dependent upon the number 

 of motor fibers involved and the rate of succession of propagated disturbance-. 

 Piper's work ( Electrophysiologic menschlicher Muskeln, Berlin, 1912) indi- 

 cates that fatigue involves a decrease in this rate rather than a reduction in the 

 total number of muscle cells activated. 



55. Munk, H. : Ueber die Folgen des Sensibilitatsverlustes der Extremist 

 fur deren Motilitat, Sitzungsber. d. Berlin Akad. Wiss., pp. 1038-1077, 1903. 



56. Sherrington, C. S. : The Integrative Action of the Nervous System. 

 London, 1911. 



57. Monakow, C. von: Aufbau und Lokalisati.m der Bewegungen brim 

 Menschen, Ber. uber d. iv. Kongress f. exp. Psychol, in Innsbruck. 1910. 



58. Sherrington. C. S. : Postural Activity of Muscle and Nerve, Brain 38: 

 191-234, 1915. 



59. Tournay, A.: Conception actuelle des grande fonctions motrice, J. de 

 Psychol. 17:904-930, 1920. 



60. Hunt. R. : The Static and Kinetic Systems of Motility. Arch. Neurol. 

 & Psychiat. 4:353, 1920. 



