498 



PHYSIOLOGY 



CHAP. 



swims normally ; buries itself at the beginning of winter; if slowly 

 lowered by a screw adjustment into water begins to swim at once 

 like an intact frog ; and is capable when the hibernating season is 

 over of feeding itself like a normal frog, by catching the flies that 

 come into its vessel. 



That the senses, particularly vision, remain intact in the frog 

 after removal of the fore-brain had already been demonstrated by 

 Desmoulins, Magendie, Longet, and others, though Flourens stated 

 the contrary. When stimulated to move, these animals are 

 capable of avoiding the obstacles they meet. Blanschko repeated 



these researches under H. Munk 

 (1880), and found that the frog 

 deprived of its hemispheres is 

 capable of adapting its move- 

 ments to different positions, 

 and to the size and nature of 

 obstacles, and to vary them 

 suitably when the power of 

 moving is interfered with, or 

 the position of the obstacles 

 changed. Such frogs are not 

 merely not blind in any ab- 

 solute sense, but they are not 

 even "psychically blind"; they 

 retain not only sensations but 

 also perceptions and visual 

 images like the intact frog. 

 The other senses are also un- 

 affected, with the exception, of 

 course, of the sense of smell, 



Fit-. 253. -Frog's brain enlarged four times. sillCe this depends Oil the 

 (Loeb.) G.C., prosencephalon ; Th.O., optic f .lf flp ^- m , v V m ll lcl w hinli nvp PY 

 thalanms: Lnb. opt., optic lobes; P. C., cere- uiaGtOiy IDS, WHICH aiC 6X- 



beiium, showing medniia obiongata below, tirpated with the fore-brain. 



whence issue the cranial nerves. TTT-I 



When the optic tlialaim are 



totally destroyed as well as the hemispheres, the animal, according 

 to Schrader, remains motionless, but this state of depression 

 partially wears off. If the animal is examined some months 

 after the operation, at the close of the winter sleep, when the 

 lesion is perfectly healed, it is seen that on gradually lowering it 

 by means of the screw into water it does not swim as when the 

 hemispheres alone are removed, but floats motionless on the 

 surface. On repeating Goltz' experiment, in which the animal is 

 made to walk up and down an inclined plane (Fig. 254), the 

 frog without a mid-brain moves its head only, and makes no 

 attempt to climb up ; if the plane is too much sloped the creature 

 crawls down instead of up, viz. behaves in a manner exactly 

 opposite to that of the frog that has lost its hemispheres only. 



