242 



AN AMERICAN TENT-BOOK OF PHYSIOLOGY. 



apply the faradic current by means of fine but blunt electrodes, the ends of 

 which are but two or three millimeters apart, to the exposed surface of the 

 cerebral hemispheres, the pia being undisturbed. Rabbits, dogs, and monkeys 

 have been the animals most commonly studied. 



If the current be slight, its application for one or more seconds causes a 

 response in the shape of movements of muscles, which are thrown into co-ordi- 

 nated contraction. The contraction continues for some time after the stim- 

 ulus has been removed. When the stimulus is very strong, instead of a lim- 

 ited and co-ordinated response, there may be a widespread contraction of 



Fig. 99.— Brain of the macaque monkey, showing the sensory and motor areas. In the sensory region 

 the name of the sensation is over the locality most closely associated with the corresponding sense-organ; 

 in the motor region the name of the part is written over the portion of the cortex which controls it. The 

 upper figure gives a lateral view of the hemisphere, and the lower a dorsal view (Beevor and Horsley). 



many muscles, resembling an epileptic convulsion. This, however, occurs 

 more commonly in the lower than in the higher mammals. On the other 

 hand, the irritability of the cortex is easily reduced, so that it becomes irre- 

 sponsive, ami often immediately after the first exposure of the brain there is 

 a time during which no response can lie obtained. 



Deferring for a moment the evidence by which the sensory characters of 

 the several areas have been established, and also the arrangements within the 

 cortex by which any group of muscles can be made to respond to stimuli 

 arriving at any sensory area, we shall follow out the distribution of those 



