FUNCTIONS OF THE CEREBRAL HEMISPHERES 515 



the resulting loss of word appreciation, sensory aphasia, will be 

 attended with great diminution of mental powers. It must be remem- 

 bered that the area of Wernicke is not a sensory centre, but a centre 

 of association betwe6n the various sense-impressions, especially those 

 of hearing and sight. It may therefore be spoken of as an intellectual 

 centre. Pure motor aphasia of course exists, but is always anarthria 

 and is due to a lesion in the lenticular zone, i.e. in the lenticular nucleus 

 and its neighbourhood, in the anterior part and the genu of the internal 

 capsule, and possibly in the external capsule. 



It is important to make a distinction between loss of sanity and 

 loss of intellectual powers. The essential factor of sensory aphasia is 

 the existence of intellectual impairment, though in his behaviour 

 the patient may appear perfectly normal. On the other hand, in 

 insanity there may be perfect retention of the intellectual processes, 

 which depend on the proper working of the lower association centres. 

 The personality of the individual, and therefore finally his behaviour, 

 involves a further association on a higher plane of these intellectual 

 processes and therefore control in accordance with the relation, past, 

 present, or future, of the individual to his environment. The pre- 

 frontal region is in all probability the seat of this highest plane of 

 association. Insanity always involves alteration of personality and 

 depends on failure of development or on disintegration processes 

 (subevolution or dissolution of this region) (Fig. 233). In monkeys 

 and cats Franz has found that destruction of the frontal lobes causes 

 a loss of recently formed habits. He concludes from his experiments 

 that the frontal lobes are the means by which we are able to learn and 

 to form habits, i.e. to regulate our behaviour in accordance with the 

 needs of our position in society. 



THE TIME RELATIONS OF CENTRAL NEURAL REACTIONS 

 In the spinal animal a stimulus of any particular quality and locali- 

 sation always evokes an appropriate reaction". A certain period of 

 time necessarily elapses between the moment at which trie stimulus 

 is applied and the moment at which the resulting reaction takes place. 

 This interval is spoken of as the simple reaction time, and in the spinal 

 animal is entirely independent of consciousness. Many reactions, 

 even in the intact animal, are also, as we may say, involuntary and are 

 not modified perceptibly by our consciousness of their occurrence : 

 such reflexes as the withdrawal of the hand when it comes in contact 

 with a hot surface, the shutting of the eyelid when the conjunctiva 

 is touched, the drawing up of the leg when the sole of the foot is tickled. 

 Not only are these carried out in the absence of voluntary impulses, 

 but in many cases it is almost, if not quite, impossible to check the 

 reaction by any effort of the will. 



