634 CEREBRAL CONVOLUTIONS. [BOOK in. 



from a withdrawal of certain normal restraining inhibitory influences. 

 We have already more than once insisted that almost any event in 

 the central nervous system is to be regarded not as the result of 

 the activity of some one isolated nervous machine, but as the out- 

 come of various conflicting processes, some positive, tending to bring 

 out the event, others negative, offering a resistance or bringing 

 inhibitory influences to bear. And it would seem that this is even 

 more true perhaps of the cerebral convolutions than of any other 

 part of the nervous system. Such a view is at all events strongly 

 supported by some observations lately made by Heidenhain. If in 

 an animal under morphia, the contractions in a muscle resulting 

 from the stimulation of the appropriate ' motor area/ by a current 

 of known strength, be recorded, the sciatic nerve then divided or 

 torn or otherwise irritated, and the motor area again stimulated 

 with the same strength of current, the contractions will be much 

 less in height, and the latent period will be much longer. This of 

 course is nothing more than an instance of somewhat ordinary inhi- 

 bition. But, in certain stages of the influence of morphia, the fol- 

 lowing remarkable result makes its appearance. If a subminimal 

 stimulus be found, that is a current of such intensity that ap- 

 plied to a motor area it will produce no movement, but if 

 increased ever so slightly will give a feeble contraction of the 

 appropriate muscles, it may be observed that a slight stimulus, 

 such as gently stroking the skin over the muscles in question, 

 or indeed some other part of the body, will render the previous 

 subminimal stimulus effective, and so call forth a movement. 

 Thus if the area experimented on be that connected with the 

 lifting of the forepaw, and the subminimal stimulus be applied to 

 the area at intervals, after several ineffective applications, a gentle 

 stroke or two over the skin of the paw will lead to the paw being 

 lifted the next time the stimulus is applied to the area. On the 

 other hand, in certain other stages of the influence of morphia, the 

 convolutions and the rest of the nervous system are in such a 

 condition that the application of even a momentary stimulus to an 

 area leads to a long-continued tonic contraction of the appropriate 

 muscles. Under these circumstances, a gentle stimulus, such as 

 stroking the skin, or blowing on the face, applied immediately 

 after the application of the electric stimulus to the area, suddenly 

 cuts short the contraction, and brings the muscles at once to rest 

 and normal flaccidity. Thus according to the condition of the 

 central nervous system (and in these instances the effect appears 

 to be dependent largely though not wholly on the condition of the 

 cerebral cortex) the same kind of stimulus, and indeed we might 

 almost say the same stimulus, will lead now to exaltation, now to 

 inhibition of a nervous action. We must not dwell on these matters 

 any further, though we might point out the interesting even if 

 partial light which they throw on the phenomena known as Hyp- 

 notism. We have introduced them chiefly to emphasize the view 



