498 PHYSIOLOGY 



animals by the injection of absinthe into a vein. During the convul- 

 sion there is a rise of blood pressuie 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 condition of excitation 

 affects also the centres from which the secretorv nerves originate, so 



*> O ' 



that there is an excessive flow of saliva, which, in the idiopathic 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 move- 

 ment after a total ablation of both cerebral hemispheres. We should 

 not expect therefore to find any lasting paralysis as a result of extirpa- 

 tion 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 em- 

 ployed 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 cariied 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, 

 corresponding 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 muscle s 

 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 hemi- 

 sphere paralysis of the leg is more marked, and the muscles of the left 

 side of the trunk are also affected. Many of these symptoms disap- 

 pear 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 



