346 THE POPULAR SCIENCE MONTHLY. 



the water, and if we set the fore-foot in motion the hind-foot immedi- 

 ately begins to move, and the animal swims. In a word, to speak 

 generally, when an animal is deprived of its cerebral lobes, if one limb 

 begins to move the others immediately follow ; if one comes to rest, 

 the others tend to cease moving. Very seldom in these animals is 

 the movement limited to a single member. This solidarity in the 

 movements distinguishes animals deprived of the cerebral lobes, not 

 only from animals with a brain, but also from those in which the spinal 

 cord is severed at top. 



In a frog with the cord cut near the cranial bulb, if we move a 

 member, it produces no eifect on the movements of the animal. If we 

 excite one foot, only the subjacent muscles contract. If the impulse is 

 stronger, the entire foot recedes, but the rest of the body is motionless. 

 A lively excitation is needed to put the other feet in motion. In a 

 word, each excitation, according to its energy, produces more or less 

 extensive movement which may be limited to a single group of mus- 

 cles. It is not so with a frog in which the spinal cord is unsevered ; 

 the movements which succeed a stimulus, whether it be strong or 

 feeble, are always movements of the whole body. 



If we put a drop of vinegar on the foot of a frog in which the cord 

 is separated from the brain, the foot retires at first, then the other foot 

 makes coordinated movements to get rid of the cause of irritation. 

 The frog which has lost only its cerebral lobes commences, on the con- 

 trary, to make many leaps ; afterward it moves only one or other of its 

 feet. In the frog where the cord is severed, to each excitation succeed 

 muscular contractions ; these are always in proportion to the energy of 

 the excitation. In the frog with the cord joined to the cerebellum 

 alone, the excitation can take place without producing movement ; 

 but, be it feeble or strong, from the moment reflex action begins the 

 result is the same a movement of the body which produces a leap. 



According to the excitation, to the kind of impression produced on 

 the sensitive nerves of the skin, and on the nerves of muscular sense, 

 there is formed among the different regions of the nervous centres a 

 common purpose, which has for its regulator the pons Varolii (bridge 

 of Varoli) and the cerebellum. 



Another interesting effect now claims our notice. Among animals 

 deprived of the cerebral lobes there is another curious and constant 

 phenomenon, the forced and continual tendency to maintain an equi- 

 librium. We have seen in the frog, the carp, the eel, the pigeon, the 

 goose, mammals, etc., that every time we disturbed their centre of 

 gravity, immediately there took place a series of coordinated move- 

 ments which have the single aim of restoring the equilibrium. A de- 

 capitated insect remains always firmly posed on his feet and can take 

 no other position. If a frog is motionless on a piece of board, and you 

 slowly lower the board in the water so that he is immersed, in most 



