THE FUNCTIONS OF THE BBAIN. 15 



monkeys, and man. But it will put us, from the outset, in 

 clear possession of some fundamental notions and distinc- 

 tions which we could otherwise not gain so well, and none 

 of which the later more completed view will overturn. 



If, then, we reduce the frog's nervous system to the 

 spinal cord alone, by making a section behind the base of 

 the skull, between the spinal cord and the medulla oblon- 

 gata, thereby cutting off the brain from all connection with 

 the rest of the body, the frog will still continue to live, but 

 with a very peculiarly modified activity. It ceases to breathe 

 or swallow ; it lies flat on its belly, and does not, like a 

 normal frog, sit up on its fore paws, though its hind legs are 

 kept, as usual, folded against its body and immediately re- 

 sume this position if drawn out. If thrown on its back, it 

 lies there quietl}-, without turning over like a normal frog. 

 Xiocomotion and voice seem entirely abolished. If we sus- 

 pend it by the nose, and irritate different portions of its 

 skin by acid, it performs a set of remarkable ' defensive ' 

 movements calculated to wipe away the irritant. Thus, if 

 the breast be touched, both fore paws will rub it vigorously; 

 if we touch the outer side of the elbow, the hind foot of the 

 same side will rise directly to the spot and wipe it. The 

 back of the foot will rub the knee if that be attacked, whilst 

 if the foot be cut aAvay, the stump will make ineffectual 

 movements, and then, in many frogs, a pause will come, as 

 if for deliberation, succeeded by a rapid passage of the 

 opposite unmutilated foot to the acidulated spot. 



The most striking character of all these movements, 

 after their teleological appropriateness, is their precision. 

 They vary, in sensitive frogs and with a proper amount of 

 irritation, so little as almost to resemble in their machine- 

 like regularity the performances of a jumping-jack, whose 

 legs must twitch whenever you pull the string. The spinal 

 cord of the frog thus contains arrangements of cells and 

 fibres fitted to convert skin irritations into movements of 

 defence. We may call it the centre for defensive movements 

 in this animal. We may indeed go farther than this, and 

 by cutting the spinal cord in various places find that its 

 separate segments are independent mechanisms, for appro- 

 priate activities of the head and of the arms and legs respec- 



