NERVE 



177 



sions, may cause the series of movements which naturally 

 follow such an impression. But these movements may also 

 be caused by directly stimulating the reacting mechanism. 



When, however, reinoval of a part of the brain causes no 

 loss of power of movement, and yet prevents a stimulus 

 frovi causing its natural response, it is justifiable to 

 conclude that that part of the brain is connected with 

 reception. 



2nd. Clinical and Patholo- 

 gical Methods. — In man, the ,.-- -.. 



chief difficulty of obtaining infor- 

 mation is in finding cases where 

 only a limited part of the brain 

 is affected. But such cases have 

 been observed. Tumours of the 

 inner aspect of an occipital lobe, 

 for instance, have been found to 

 be associated with loss of visual 

 sensations without loss of mus- 

 cular power, and thus the con- 

 clusion has been drawn that this 

 part of the occipital lobe is the 

 receiving mechanism for stimuli 

 from the eyes. 



2>rd. Pathological. — As a 

 result of the destruction of 



certain parts of the nervous Fig. 88.— Diagram to Illustrate 



system, in the region of the 



thalamus, either by experiment 



in the lower animals or by disease 



in man, a degeneration of nerve 



fibres may occur to some definite 



region of the cortex, and this generally shows that the area 



is a receiving one. 



^th. Anatomical Methods. — When it has been found 



possible to assign a definite function to any area of the 



cortex, its extent and limits may be determined by the 



extent and distribution of the particular character of the 



arrangement and structure of the nerve cells. 

 12 



Different possible Channels of 

 Cerebral Response to Stimula- 

 tion, and to show how, through 

 reflex action of the lower arcs, 

 the action of the higher arcs 

 may be simulated. 



