CONTRIBUTIONS FROM PAWLOW'S LABORATORY 375 



portant, draws to itself the available nervous energy, leaving 

 thereby other centres ineffective. The force of this interpre- 

 tation is easily recognized by a modification of the above ex- 

 periment. If, instead of food, an acid is used in stimulating 

 the salivary gland — the acid likewise being an unconditioned 

 stimulus of salivary secretion, but one which is ordinarily 

 rejected by the animal — the painful sensation of the electric 

 current can not be overcome nor can a conditioned salivary 

 reflex be developed under these circumstances. 



Many seemingly miraculous events of human experience 

 become intelligible in the light of these experiments. The 

 mutilation of the body practiced by certain sects in an ecstasy 

 of religious fervour, the apparent insensitiveness to excruciating 

 pain demonstrated by many martyrs of a creed or ideal, absolute 

 disregard of fatal injuries when the nervous energy is mustered 

 in a life or death struggle — these and many others are phenomena 

 obeying definite physiological laws. 



If we reflect upon what has been said and fix our attention on 

 the thing which is common to all these diverse facts the conclusion 

 will not be unwarranted that the function of the higher centres 

 of the brain is governed by a fundamental principle of the flow 

 of nervous energy towards points of the highest irritation. 



Consciousness and unconsciousness, according to Pawlow, are 

 purely physiological phenomena of the same order. Conscious- 

 ness is a state of a part of the large hemispheres characterized by 

 an optimum affectibility. At a given time and under given 

 circumstances new conditioned reflexes and differentiation of 

 conditioned stimuli develop here rapidly. This is, therefore, the 

 creative centre of the hemispheres at the particular moment. 

 All other parts of the hemispheres are in state of diminished 

 affectibility. Only stereotyped, long established conditioned 

 reflexes are displayed there at that moment; they are the seat 

 of unconscious processes. The distribution of parts of optimum 

 and minimum susceptibility in the hemispheres is not fixed; 



Pawlow's frequent use of the term " centre." Nowhere, so far as I know, does he 

 commit himself definitely to the question of localization of centres in the brain. 

 It is clear none the less that he assumes localization only in the broadest sense. 

 Centres are to him physiological entities rather than anatomically distinct areas. 

 Since every point of an analyser has a corresponding cell in the cortex, the impulses 

 from a certain analyser naturally travel to a definite region in the hemispheres. 

 But there is also much interlocking between adjacent centres which seem to wedge 

 into each other. Besides, the cortical elements seem to be functionally interchange- 

 able, at any rate his extirpation experiments bear out such a conclusion. 



