274 COMPARATIVE PHYSIOLOGY OF THE BRAIN 



powers were only suppressed or inhibited temporarily 

 by the lesion of the spinal cord." The same is true 

 in regard to the vasomotors. Division of the spinal 

 cord reduces the tonus of the blood-vessels of the 

 posterior legs. After a time the blood-vessels recover 

 and become normal again. Now if the sciatic nerve 

 in the same animal be severed, a new temporary para- 

 lysis of the vasomotors follows. This proves that 

 the vasomotor paralysis in the hind-legs that occurs 

 after the division of the spinal cord is due to a 

 shock-effect of the operation. What the nature of 

 this shock-effect is we do not know. Perhaps v. 

 Cyon's experiment throws light on this : v. Cyon 

 showed, namely, that the tension of the muscles de- 

 creases after the division of the posterior root of their 

 segment (3). 



8. We conclude from all these observations on dogs 

 that small lesions do not cause any disturbances in the 

 processes of associative memory, and that Hitzig and 

 Munk are wrong in interpreting the disturbances fol- 

 lowing the excision of a small piece of the cortex as 

 psychic disturbances. In the majority of cases such 

 slight lesions cause no disturbance, and where any 

 is caused it is of such a character as could be pro- 

 duced by the lesion of a peripheral nerve. If we wish 

 to produce psychic disturbances by a lesion of the 

 brain, we must destroy extensive parts of both hemi- 

 spheres. Operations in one hemisphere alone, and 

 even the destruction of an entire hemisphere, have no 

 such effect. 



