162 ADVANCED LESSONS IN PRACTICAL PHYSIOLOGY 



of this frog. Observe that the decerebrated animal produces a peculiar 

 sound whenever touched. The same result may be obtained by grasp- 

 ing the frog in such a way that your thumb and index-finger come to 

 lie laterally upon the abdomen. Stimulate a normal frog in the same 

 manner. Compare. 



Annotation. The test described last is one of the best means of ascertaining the 

 function of the cerebrum. In the normal animal the act of croaking is under the 

 control of the cerebral hemispheres, i. e., it is an associated act. Consequently, it 

 will be almost impossible to evoke it by inadequate stimuli. The removal of the 

 cerebrum, on the other hand, changes this complex act into a simple reflex. The 

 influence of the higher centers having been destroyed, it may then be evoked by 

 ordinary stimuli in a reflex way. 



A male frog may be recognized by the cushion-like thickening at the base of 

 the innermost digit of the hand. Besides, the male rana esculenta possesses a 

 bladder-like resonating pouch on each side of the mouth. 



Attention should also be called to the fact that an animal without cerebral 

 hemispheres is incapable of "feeling." The sensorium ceases to exist after the 

 removal of these structures, and only the ordinary reflex sensory mechanism remains 

 behind. 



8. Influence of the Cerebrum. Place a normal frog in a basin filled 

 with water. Warm the water slowly, and note that the frog will make 

 complex efforts to escape as soon as the temperature of this medium 

 has risen to about 25 C. 



Place a frog, the cerebrum of which has been destroyed, in cold 

 water. Warm the water to 40 C., and observe the reflex movements 

 resulting in consequence of the thermal stimulation. While this ani- 

 mal may escape from the basin, this result is accidental, and is due 

 solely to the reflex contractions of the muscles. 



