THE GENERAL FUNCTION OF THE CEREBRUM 669 



Quite similarly, a decerebrated frog 1 shows few modifications in 

 its behavior, excepting those directly referable to the loss of the sense 

 of smell. It retains a normal posture and jumps and swims normally. 

 It rights itself when placed upon its back, and executes centrifugal 

 and balancing motions when placed upon a rotating disc. Provided 

 that the thalamus has not been injured, it avoids obstacles placed in 

 its way, and reacts to stimuli applied to the nasal mucous membrane by 

 various protective movements. These reactions, however, it shows 

 only when stimulated. Its normal attitude is one of inactivity, 'be- 

 cause it has lost the memory of past experiences and instincts. For 

 this reason, it need not surprise us that an animal of this kind takes no 

 food but must be fed; in fact, the food must be placed directly into its 

 mouth. The processes of deglutition and digestion are in no way 

 impaired, and hence, it is possible to keep this animal for many months 

 or even for years. A general idea regarding the function of the cere- 

 brum may be had from the character of the croaking reflex before and 

 after the removal of the hemispheres. Under normal conditions, this 

 act is a complex association phenomenon; i.e., this sound is produced 

 only in consequence of definite cortical processes, and is under the 

 guidance of the will. In the absence of the cerebrum, on the other 

 hand, it is a pure reflex, so that it may be elicited at any time by the 

 proper kind of stimulation consisting in a gentle pressure upon the 

 lateral aspects of the chest and abdomen. Furthermore, if we pass 

 our hand over a number of normal frogs, these animals will immediately 

 make motor efforts to escape from the area of stimulation, while the 

 decerebrated animals will not. In brief, we may say that the latter 

 have lost their associations and are no longer under the control of 

 motives or sensations of fear. 



The same general effects are manifested by birds 2 when deprived 

 of their cerebral hemispheres. They assume a position of rest, generally 

 upon one leg with the head drawn in and the bill buried in the 

 feathers. Every now and then they will open their eyes, stretch 

 themselves, and walk about in the cage. This nonresponsive attitude 

 may be disturbed at any time by stimulation, i.e., the animal may 

 be made to fly by throwing it some distance into the air, or it may be 

 made to execute balancing movements upon a rope swung back and 

 forth. It will right itself immediately if placed upon its back, and 

 continues to move about if made to do so. In all these cases, however, 

 the position of rest is sought very soon after the stimulation ceases. 

 Its reactions are machine-like, and are executed without definite purpose 

 or regard to environment. This is well shown by the decerebrated 

 pigeon which, when made to fly, soon alights upon any object situated 

 in its path even if it should endanger its life. As all its digestive 

 processes and spinal reflexes are perfectly normal, this pigeon may be 

 kept for an indefinite period of time provided, of course, that it is 



1 Blaschko, Sehzentrum der Frosche, Berlin, 1880. 

 2 Bechterew, Archiv fur Physiol., 1890, 489. 



