ix MID- AND INTEK-BKAIN 505 



brain. In the absence of adequate researches, it is not at present 

 possible to distinguish which portion of these functions belong to 

 the 'tween-braiu, but it may be assumed with great probability 

 that Flourens' classical description of the pigeon destitute of 

 sensation and spontaneous movements corresponds with what is 

 observed when the inter -brain is destroyed along with the 

 fore-brain. Certain observations made by Schrader on pigeons 

 in which ablation of the hemispheres was associated with very 

 extensive lesions of the optic thalami, tend to confirm this opinion. 

 He found that under these conditions the animal collided with 

 obstacles, and was unable promptly to correct slight passive dis- 

 placements of the extremities. 



VI. The effects of total destruction of the cef ebrum in small 

 mammals was frequently investigated by Floiirens ; but it was 

 reserved for later observers to give an accurate account of them. 



On this point again the results obtained by H. Mnnk are in 

 fundamental contradiction with those of other workers. He 

 experimented on rabbits, guinea-pigs, and rats. The first, 

 according to Munk, survive at most two days ; guinea-pigs and 

 rats four days. Death is not due to inanition, because they lose 

 only 7 to 20 per cent of their weight ; but to inflammatory reaction 

 and progressive softening of the remaining parts of the brain. 



In the first stage the decerebrated animal remains motionless 

 and passive like Flourens' pigeons. In the second stage the 

 animal makes a few rare isolated movements, occasionally a few 

 steps to left or right. Eespiration is quicker and deeper, and 

 after a few hours the animal begins to walk. The third stage is 

 characterised by periodic walking, such as Fano described in the 

 brainless tortoise. In rabbits, guinea-pigs, and rats, when deprived 

 of the prosencephalon, the pupil reflexes persist but the animals 

 are not otherwise affected by light. In walking they collide with 

 every obstacle they meet, go straight ahead without altering their 

 course, and run up against the wall of the room, or fall off the 

 table, in short, they show complete lack of the visual sense. 



Widely different and, as regards vision, exactly contrary 

 results were obtained by Christian! in rabbits after excision of the 

 cerebral hemispheres, including the corpora striata, but sparing 

 the optic thalami. Directly after the operation the animal 

 remains motionless, but it escapes if excited. If kept awake it is 

 capable of spontaneous movement, but relapses into sleep if left 

 alone. In provoked or spontaneous movements nothing abnormal 

 occurs ; the animal avoids obstacles without touching them with 

 its nose, and is even capable of jumping up and climbing without 

 stumbling. Obviously, therefore, its movements are guided by 

 the sense of vision. 



If in addition to the prosencephalon the thalamencephalon 

 also is extirpated or profoundly injured, Christian! noted that the 



