REMOVAL OF BOTH CEREBRAL HEMISPHERES. 699 



ascend to the surface to breathe. And not merely so, but if placed in 

 a vessel inverted over a pneumatic trough, and containing a column of 

 water sustained by barometric pressure, it will ascend to the surface as 

 before ; but not rinding there the necessary atmospheric air, will work 

 its way downwards, and succeed in making its escape out of the vessel 

 to the free surface of the trough. There is a method in its movements. 

 If an obstacle be placed between it and the light of a window, the frog 

 will not spring blindly against it when its toe is pinched, but will clear 

 it or spring to the side. It will alter the course of its leap, according 

 to the position of the obstacle between it and the light. There is, 

 so far, no difference between its behaviour and that of a frog in full 

 possession of all its faculties. But yet a very remarkable difference is 

 perceptible. The brainless frog, unless disturbed by any form of 

 peripheral stimulus, will sit for ever quiet in the same place, and 

 become converted into a mummy. All spontaneous action is an- 

 nihilated. Its past experience has been blotted out, and it exhibits no 

 fear in circumstances which otherwise would cause it to retire or flee 

 from danger. It will sit quite still if the hand be put forth cautiously 

 to seize it, but will retreat if a brusque movement is made close to its 

 eyes. Surrounded by plenty, it will die of starvation ; but, unlike 

 Tantalus, it has no psychical suffering, no desire, and no will, to supply 

 its physical wants." 



There is a good deal of difference manifested if care be taken 

 not to injure the optic thalami in removing the hemispheres. 1 Under 

 these circumstances, the frog, after the first effects of the operation 

 have passed off, will show spontaneous movements without any manifest 

 external stimulus, 2 will feed itself by catching insects and the like, 

 will bury itself on the approach of winter, in order to hibernate, and 

 resume activity with the advent of spring, and in the breeding-season 

 will give evidence of possessing normal sexual instincts. All these 

 manifestations, as well as the power of balancing itself on a tilted 

 board and the reaction on a turn-table, are either abolished or rendered 

 imperfect on removing the optic thalami as well as the hemispheres. 

 The latter are, in the frog, only to a very small degree developed, 

 containing but a single layer of nerve cells ; the thalami, on the other 

 hand, are, in this animal, the chief centres for movements which are 

 apparently voluntary, an importance which they probably owe to their 

 connection with the visual organs on the one hand, and the tactile 

 sense on the other, these being the senses by which the movements of 

 these animals are mainly directed. 



" The results which have been observed in fishes after similar 

 ablation of the cerebral hemispheres are, cceteris paribus, of the same 

 nature as those seen in frogs. A fish so mutilated 3 maintains its 

 normal equilibrium in the water, and uses its tail and fins in swimming 

 with as great precision and co-ordination as before. The brainless fish 

 is, however, continually on the move, and there is also method in its 

 movements. It will not run its head against any obstacle placed in its 

 path, but turns to the right or left according to circumstances. Left to 



1 Schrader, Arch. f. d. gcs. Physiol, Bonn, 1887, Bd. xli. S. 75; J. Steiner, "Die 

 Functionen d. Centralnervensystem, u.s.w.," Erste Abth. " Der Froscli," Braunschweig, 

 1885. 



• This had already been shown by Desmoulina and Magendie, ' Des systemes nerveux," 

 1825, tome ii. p. 626. 



3 Vulpian, " Lecons sur la physiol. du systeme nerveux," Paris, 1866, j). 683. 



