Instability of Cortical Points. 



251 



what degree the reaction obtained from one and the same topographical point 

 of the cortex may vary from time to time. 



In doing so, we are following a trend of enquiry very noticeable in recent 

 experimental study of reflex and other nervous reactions. The reversal 

 (" Uinkehr ") of the sense of the movement elicited by identical stimulations 

 of the same reflex preparation as determined by this or that accessory change 

 in the other conditions of the experiment has been a frequent theme in 

 recent papers. Such observations, besides tending to throw light on the 

 reflex working of the neural machinery, have the further interest that they 

 tend — although perhaps remotely — to make some approach towards study of 

 the physiological conditions which underlie " will," if so bold a use of the 

 term may be allowed. 



Variations of the muscular response given by one and the same point of 

 the motor cortex conformably with variations in the degree of narcosis, etc., 

 have been met often in our observations. Such have frequently been 

 described by other experimenters ; and, since they are well known, we do not 

 intend to discuss them now. We wish, however, to call attention to some 

 other sources of variability of the cortical responses, instances of alteration 

 and of reversal more closely analogous to those recently studied in the case 

 of reflex preparations. 



II. Methods Employed. 



The material used in these present observations has been provided entirely 

 by the monkeys and the anthropoid apes. One chimpanzee (Troglodytes 

 niger) has been used, one baboon (Papio anubis), and the remainder ordinary 

 small monkeys (Macacus rliesus, Macacus sinicus, Callothrix). All of the 

 experiments were done under chloroform and ether narcosis. 



For the purposes of graphic registration (as in the majority of the 

 observations), two muscles which antagonise each other at the elbow — 

 supinator longus and the humeral head of the triceps — have been used. 

 These have been isolated, and the complication of movement of other than 

 the selected parts has been abolished — by the motor paralysis of the other 

 muscles at the shoulder, elbow, and wrist. The muscles so treated have 

 been — trapezius, deltoid, supraspinatus, infraspinatus, teres major, teres 

 minor, latissimus dorsi, scapular head of triceps, pectoralis major, pectoralis 

 minor, biceps, and coraco-brachialis, and all the muscles of the fore-arm with 

 the exception of the supinator longus. The lower end of triceps has been 

 freed by division of the olecranon process and connected directly by a thread 

 with one of the recording levers. The supinator longus has not, however, 

 been interfered with, but the elbow has been allowed to swing free, and the 



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