NERVE 185 



3. Storing and Associating Part of the Cortex. 



The existence of a special part or parts of the brain 

 connected with the storing of impressions, so that they 

 may be associated with present sensations, is indicated 

 by the following considerations : — It is this association of 

 present stimuli with past sensations which is the basis of 

 intellectual life, and in man the frontal and parietal lobes of 

 the brain are much more developed than in the lower animals. 

 So far, stimulation of these has failed to give any indication 

 of resulting sensations, or to produce muscular movements. 

 They may be extensively injured without loss of sensation 

 and without paralysis, and hence it has been concluded that 

 the storing and associating functions must be chiefly located 

 in them. 



In these regions the nerve fibres acquire their medullary 

 sheath at a very late date. 



4. The Relationship of Consciousness to Cerebral Action. 



Cerebral action frequently goes on without consciousness 

 being implicated : but, so far as we know, consciousness 

 without accompanying cerebral action is unknown, and there 

 is evidence that it is only when the actions of the various 

 parts of the cerebrum are co-ordinated that consciousness is 

 possible. In cases of Jacksonian epilepsy, as a result of a 

 small centre of irritation on the surface of the brain, a 

 violently excessive action of the cerebral neurons starts at 

 the part irritated and passes to involve more and more of the 

 brain. In such fits, it is found that at first the patient's 

 consciousness is not lost, but that, when a sufficient area of 

 brain is involved in this excessive and inco-ordinated action, 

 consciousness disappears. 



Unconsciousness may be produced by many conditions 

 which modify the nutrition of the brain. (1) Many drugs, 

 of which chloroform and ether may be taken as types, poison 

 the brain and cause loss of consciousness, (2) Similar 

 poisons may develop in the body as the result of faulty 

 metabolism, as is seen in diabetic coma. (3) A sudden 

 failure of the supply of blood to the higher centres may 

 cause the loss of consciousness which occurs in fainting. 



