470 
DR. D. PERRIER ON THE BRAIN OE MONKEYS. 
This experiment indicates with precision the region in the temporo-sphenoidal whose 
destruction is followed by impairment or total abolition of tactile sensation. 
In the various cases in which this result 
followed extensive lesion of the temporo- 
sphenoidal lobe, it was found that the hippo- 
campus major and the hippocampal convo- 
lution were more or less extensively involved. 
The destruction of these convolutions alone, 
as shown by this experiment, abolishes tac- 
tile sensation alone. 
To ascertain the existence or absence of 
this sense is surrounded with some difficulty, 
owing to the fact that reflex reaction may 
simulate the appearance of tactile sensation, 
properly so called. The mere fact of reaction to a stimulus is no proof of the existence 
of sensation. 
The entire absence of reaction, however, observed in some of the preceding experi- 
ments, where the hippocampal region was completely destroyed, is a strong proof of the 
abolition of sensation, when it is considered that reaction was lively and marked on the 
opposite side of the body at the same time. 
But the loss of tactile sensation is even more conclusively indicated by the fact that 
monkeys in whom the hippocampal region was destroyed ceased to use the opposite 
limbs for the purposes of prehension or the exercise of the faculty of touch. 
To react to tactile stimuli may signify reflex action or tactile sensation, or both ; to 
touch necessarily implies the possession of the power of tactile perception. 
The condition of the limbs in these cases was such as to simulate motor paralysis ; and 
it is well known that Sir Charles Bell mistook the immobility of the side of the face 
resulting from anaesthesia caused by division of sensory branches of the fifth for real 
motor paralysis. It was pointed out by Mayo that, owing to the loss of tactile sensation, 
an animal has no indication for the regulation and adaptation of its muscular movements, 
and hence ceases to make them. That anaesthesia, and not motor paralysis, existed on 
the side opposite the destruction of the hippocampus, is shown by the fact that a certain 
degree of voluntary motion was retained. The animal (Exp. XVIII.) whose leg was 
anaesthetic could replace it on the perch, though it continually tended to slip off when 
the animal withdrew its attention from it. 
There was no muscular flaccidity as in true motor paralysis, nor was there any appear- 
ance of facial distortion, such as would have been produced by motor paralysis of one side. 
It is impossible to differentiate between lesion of the hippocampus itself and of the 
hippocampal or uncinate convolution. A lesion involving the hippocampus necessarily 
involves the medullary aspect of the uncinate convolution, and it is impossible to destroy 
the uncinate convolution without injuring the hippocampus. 
Pig. 24. 
Pig. 24 represents by the shading the external 
extent of the lesion in the uncinate convolution, and 
the dotted lines the track of the sinus caused by the 
cautery in Experiment XYIII. 
