16 
PROFESSORS V. HORSLEY AND E. A. SCHAFER 
also by loss of general sensibility of the paralysed part. At the same time there is 
often undoubted diminution of reaction to stimuli of various kinds (touch, prick, hot 
wire, electric shocks), but it is impossible to say how far this may indicate a corres- 
ponding diminution of sensibility. Monkeys present very great differences in the 
degree to which they exhibit emotion, some being habitually dull and stupid, while 
others are lively and mercurial in temperament. In those belonging to the former 
class it is often difficult to elicit any information from the expression of the face, so 
that an irritation of the paralysed limb, insufficient to cause general movement of the 
body, does not provoke any indication of perception. On the other hand, in lively 
Monkeys we have often obtained, as the result of even slight irritation of paralysed 
parts, unmistakable signs of perception, and in cases of this kind in animals one 
positive observation must be regarded as of greater importance than many negative 
statements. But in dealing with questions of sensibility the resalts of experiments 
upon animals must always be to a certain extent unsatisfactory, since we can obtain 
no evidence of the actual character of the sensation provoked. Fortunately it is 
probable that the elucidation of this question by careful observations of cases of 
cerebral injury in Man will not long be wanting. 
Difficult as it is to decide in animals questions relating to the general and tactile 
sensibility of a limb deprived of voluntary motion, it is yet more difficult to form any 
opinion regarding the presence or absence of the so-called muscular sense. It was the 
opinion of Hitzig that a lesion of the motor cortex effected an abolition of the 
muscular sense of the part paralysed, and he inclined to regard the paralysis as 
produced rather in consequence of the loss of this directive sensation than immediately 
by removal of motor nerve-cells. This mode of viewing the question and of explaining 
the facts of experiment has been adopted and ably advocated by Bastian, who brings 
forward a large amount of evidence derived from pathological observation in its 
favour.* Terrier, on the other hand, appears to admit only the direct production of 
motor paralysis, and is disposed to localise all kinds of sensibility, including the 
muscular sense (which he regards as entirely derived from indications conveyed by 
nerves of ordinary tactile sensibility) in other regions of the cortex than those 
connected with the production of voluntary motion ; while others, again, amongst whom 
ScHiFF and MuNK are to be included, endeavour to show that, while from one set of 
nerve-cells of the excitable regions of the cortex the fibres which convey voluntary 
impressions may directly arise, other cells of the same regions, indirectly connected 
with the first set, may serve as the terminal organs of the nerve-fibres, which convey 
sensory impressions, general, tactile, and muscular, and may transfer these centrifugal 
impressions to cells which give origin to the fibres of the motor tract. And it would 
appear that, in connection with this view, those who advocate it are for the most part 
* 'Brain as an Organ of Mind.' See also liis article on Motor Centres and the Muscular Sense 
in a recent number of ' Brain.' 
