586 PHYSIOLOGY CHAP. 



sensibility and motion." They diminish gradually, and by the 

 second week the dog begins to recognise contacts on the skin of 

 the right fore -leg. The gait, too, improves. After four weeks 

 only a certain defect in the isolated movements of this limb can be 

 perceived, with a slight lack of precision and dexterity in the com- 

 plicated movements of locomotion. Even these small disturbances, 

 however, have disappeared ten weeks after the operation. 



Very different are the effects of total or partial removal of the 

 excitable area of the cortex in the ape. Goltz described a Macacus, 

 in which the cortex of the frontal and parietal lobes of the left 

 hemisphere was destroyed by two operations. This monkey was 

 kept under observation for eleven years. Completely hemiplegic 

 immediately after the operation, after a few months it was only 

 hemiparetic in all the muscles of the right side. In slow walking 

 it used both feet and the left hand, while the right hand was 

 generally held up in the air. In scratching and for grasping the 

 food offered to it, it always used the left hand. 



The clumsy, imperfect manner in which the right limbs were 

 used in walking, jumping, and climbing, showed that cutaneous 

 and muscular sensibility were affected. In fact, the ape did not 

 recognise slight contacts on the skin of the right limbs, while the 

 same contacts were readily appreciated on the left. But the skin 

 of the right side was not entirely insensitive ; moderate pressure on 

 the right paw was plainly felt by the animal, which showed that it 

 was able to localise it. 



The inability to use the right hand in isolated purposive acts 

 depends partially on the blunting of cutaneous sensibility. If the 

 monkey is offered a large apple which it cannot hold with the left 

 hand alone, it uses the right hand as well to lift it to its mouth. 

 If the left hand is held while the monkey is offered a piece of sugar, 

 it stretches out its right hand slowly, evidently overcoming some 

 resistance to the voluntary impulses. By repeated efforts it can 

 learn once more to give its right hand and make a military salute 

 with it ; but the use of the right hand always remains a difficulty. 

 Some effort is evidently required to extend the fingers completely 

 and grasp objects with them, which implies a commencing con- 

 tracture of their muscles. The great difference in the power of using 

 the two hands is shown by the following experiment : if the monkey 

 is set on a table and its left hand held while some cherries are 

 thrown down in front of it, the animal will carefully and clumsily 

 use its right hand to take them one after another and put them 

 in its mouth. But as soon as the left hand is liberated it uses it 

 with astonishing dexterity to catch up the fruit. 



These observations, as a whole, show that the excitable area is 

 more important in the monkey than in the dog for the normal 

 control of the muscles. Years after the operation, residual 

 phenomena of deficiency are recognisable in apes as a slight degree 



