CENTRAL NERVOUS SYSTEM. 



The existing symptoms arc not intensified by the removal of the remaining 



half. The permanent condition of the muscles after operation is expressed 

 l>v an atonia, or lack of tonus, in the resting muscles ; an asthenia, or loss of 

 strength, which was measured by Luciani,and was most marked in the hind- 

 leg; an astasia, or a lack of steadiness in the muscles during action; and 

 finally an ataxia, or a want of orderly sequence, in the contraction- of the 

 muscle-groups. The general expression of these symptom is a twisl of the 

 trunk, the concavity being toward the operated side, combined with a dis- 

 orderly gait. At the same time there is no demonstrable permanent dis- 

 turbance of tactile or muscular sensibility. 



Though the two halves of the cerebellum are united by strong commis- 

 sural fibres, the complete division of the organ in the middle line is followed 

 by a disturbance of the gait which is only transitory. Hence it is inferred 

 that the connections of the cerebellum are mainly with the same side of the 

 bulb and spinal cord. Cephalad of the cerebellum the connection, however, 

 is a crossed one, each cerebellar hemisphere being associated with the contra- 

 lateral cerebral hemisphere. Throughout these connections, both cephalad 

 and caudad to the cerebellum itself, it appears that there is always a double 

 pathway, and the cerebellum not only sends impulses to, but receives them 

 from, the regions with which it is associated. 



One effect of removal of one-half of the cerebellum is to increase the re- 

 sponsiveness of the cortex of the contra-lateral cerebral hemisphere to electri- 

 cal stimulation, thereby making it possible with a weaker stimulus to obtain 

 a reaction which could be obtained from the other hemisphere only with a 

 stronger one. When an irritative lesion is made, instead of a merely de- 

 structive one, the rotation and falling are away from the side of the lesion, 

 instead of toward it. 



The experiments altogether -how the cerebellum to be closely associated 

 with the proper contraction of the muscles, and this i> so directly connected 

 with the maintenance of equilibrium ' that it is not surprising to find that 

 stimulation or removal of the cerebellar cortex, besides producing nystagmus, 

 may give rise to deviations of the eyes similar to those found on injury of the 

 semicircular canals or stimulation of their nerves in fishes. 2 



PART III.— PHYSIOLOGY OF TliE NERVOUS SYSTEM TAKEN 



AS A WHOLE. 



A. Weight of the Brain and Spinal Cord. 



In attributing a value to the mass of the nervous system we assume that 

 the elements which compose it possc-s potential energy. This energy varies 

 for any given element in accordance with :i number of conditions, but for the 

 moment it will be sufficient to point out that if the mass of the entire system 

 is significant the masses of its respective subdivisions are also significant, as 



1 A. Thomas: " Le Cervelet," F.uu], anafomique, dinigue et physiologique, Paris, 1897. 



2 Lee: Journal of Physiology, 1893, vol. sv. ; 1894, vol. wii. 



Vol. II.— IS 



