THE CENTRAL NERVOUS SYSTEM 841 



skin, particularly in the region of the head, is mechanically or 

 electrically stimulated. The normal Necturus, on the other 

 hand, lies for long periods with its gills at perfect rest, and when 

 stimulated, moves for a considerable distance.* After a time, 

 two months or more it is true the brainless frog, if it be 

 kept alive, as may be done by careful attention, will recover 

 a certain portion of the powers which it has lost by removal of 

 the cerebral hemispheres ; and, indeed, the longer it lives, the 

 nearer it approximates to the condition of a normal frog. A 

 brainless frog has been seen to catch flies and to bury itself as 

 winter drew on. A fish even three days after the destruction of 

 its cerebrum has been seen to dart upon a worm, seize it before 

 it had time to sink to the bottom of the aquarium, and swallow 

 it. Even in the pigeon the loss of the hemispheres, which at 

 first induces a state of profound and seemingly permanent 

 lethargy, is to a great extent compensated for, as time passes 

 on, by the unfolding in the lower centres of capabilities pre- 

 viously dormant or suppressed. A brainless pigeon has been 

 known to come at the whistle of the attendant and follow him 

 through the whole house. 



In the mammal the removal of the whole or the greater part of 

 the cerebral hemispheres at a single operation is uniformly and 

 speedily fatal ; even rabbits or rats, which bear the operation 

 best, survive but a few hours. During those hours they manifest 

 phenomena similar to those observed in the bird and the frog. 

 In the dog the entire cortex has been removed piecemeal by 

 successive 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 brain- 

 less frog ; but in favourable cases, even in the dog, the move- 

 ments 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, nor of carrying on mental operations of a low intel- 

 * Personal observations. 



