gi6 THE CENTRAL NERVOUS SYSTEM 



operations. In this case, of course, the change in the condition of 

 the animal is more gradually produced, and an opportunity is 

 afforded for a certain recovery of function in the intervals between 

 the operations. On the whole, however, as might be expected 

 from its greater intellectual development, recovery is more imperfect 

 in the dog than in the bird, much more imperfect than in the frog. 

 But even in the dog wonderful resources lie hidden in the grey 

 matter of the central neural axis, and are called forth by degrees 

 to replace the lost powers of the cerebral cortex. It is true that a 

 brainless dog is a less efficient animal than a brainless fish, or even 

 than a brainless frog; but in favourable cases, even in the dog, the 

 movements of walking may still be carried out with tolerable pre- 

 cision in the absence of the cerebral hemispheres. The animal can 

 swallow food pushed well back into the mouth, although it cannot 

 feed itself. Stupid and listless as it is compared with the normal 

 dog, it seems to be by no means devoid of the power of experiencing 

 sensations as the result of impressions from without, or of carrying 

 on mental operations of a low intellectual grade. Goltz had a dog 

 which lived more than a year and a half practically without its 

 cerebral hemispheres, and another which lived thirteen weeks. 

 He believes that they had lost understanding, re flection, and memory, 

 but not sensation, special or general, nor emotions and voluntary 

 power. Their condition may be best described as one of general 

 imbecility. Hunger and thirst are present. They experience satis- 

 faction when fed, become angry when attacked, see a very bright 

 light, avoid obstacles, hear loud sounds, such as those produced 

 by a fog-horn, and can be awakened by them. They are not com- 

 pletely deprived of sensations of taste and touch. But it ought to 

 be remembered that the interpretation of the objective signs of 

 sensation in animals is beset with difficulties; and although every- 

 body admits the accuracy of Goltz's description of what is to be 

 seen, his interpretation of the facts has been severely criticized, 

 particularly by H. Munk. 



To the monkey there can be no doubt that the loss of the cerebral 

 hemispheres would be a still heavier and more irremediable blow 

 than to the dog. But nobody has yet succeeded in keeping a 

 monkey alive after complete removal of even one hemisphere. 



In man the destruction of considerable masses of brain-substance, 

 particularly if gradual, is not necessarily fatal. How great a loss 

 is compatible with life cannot be exactly stated. It depends to a 

 large extent on the position of the lesion. But it is possible that 

 one cerebral hemisphere may be rendered functionally useless 

 without immediately putting a term to existence. In the foetus, 

 however, no portion of the great brain is absolutely indispensable for 

 life and movement. An anencephalous foetus (in which the brain has 

 remained undeveloped) may be born alive, and live for a short time 





