440 PHYSIOLOGY 



epileptic convulsions can be excited in animals by the injection of absinthe 

 into a vein. During the convulsion there is a rise of blood pressure and a 

 quickening of the pulse ; the respiration is very often stopped during the tonic 

 part of the spasm, so that the patient becomes livid. The universal con- 

 dition of excitation affects also the centres from which the secretory nerves 

 originate, so that there is an excessive flow of saliva, which, in the idio- 

 pathic case, is responsible for the characteristic frothing at the mouth. 



EFFECTS OF ABLATION OF THE MOTOR CENTRES 

 We have seen that a dog may preserve complete power of movement 

 after a total ablation of both cerebral hemispheres. We should not expect 

 therefore to find any lasting paralysis as a result of extirpation of portions 

 of the brain, such as the motor centres. Ablation of the motor areas in 

 these animals, during the first few weeks after the operation, gives rise to 

 considerable disorders of movement, the muscles on the side of the body 

 opposite to the lesion being markedly weaker than those on the same side. 

 These symptoms, however, gradually pass off, so that after a time not only 

 are both limbs employed in the ordinary automatic movements of progression, 

 but the animal can be taught new movements in the limb, the cortical centre 

 for which has been excised. We must conclude therefore that in the dog all 

 the movements, including those which are voluntary and conscious, can be 

 carried out in the absence of the motor centres, although destruction of these 

 centres may impair the accuracy with which some of the finer movements are 

 regulated. 



In the monkey (Macacus) the effect of ablation is more marked, corre- 

 sponding to the greater degree of localisation in these animals. If the whole 

 of the motor area on the external surface of the brain be excised, e.g. on the 

 right side, there will be almost complete paralysis of the left arm and the left 

 side of the face, and weakness of the muscles of the left leg. The animal 

 will continue to use the leg in walking and in climbing. If the lesion extends 

 to the medial side of the hemisphere paralysis of the leg is more marked, and 

 the muscles of the left side of the trunk are also affected. Many of these 

 symptoms disappear in the course of time. In a monkey in which Goltz had 

 destroyed the greater part of the left side of the cerebral hemispheres it was 

 found that the right arm and hand could be still employed alone for such 

 purposes as taking food, although the movements were much more awkward 

 than those of the left hand. 



Still less complete is the recovery from lesions of the motor area in man. 

 We possess now a considerable number of typical histories of cases in which 

 part of the motor cortex has been destroyed by disease or by operation, and 

 the seat of the lesion verified by post-mortem examination. In all these 

 cases there has been a loss of voluntary movement corresponding in distribu- 

 tion to the seat of the lesion and proportionate in its severity to the extent 

 of the lesion. On the other hand, equally extensive lesions outside the as- 

 cending frontal convolution have been shown to have no effect on voluntary 

 movements. The loss of movement is chiefly confined to those which we 



