302 [RELATIONS OF THE SPINAL CORD AND BRAIN. N 



Increase of aggerated in certain conditions of disease, as, for example, in 

 spinal action, tetanus, in which the slightest peripheral irritation may be 

 followed by violent convulsive movement, or the same occurs by the 

 agency of powerful poisonous substances, as strychnine. In these cases 

 the action may be either limited simply to the cord, as in the tetanus 

 brought on by opium in frogs, or the brain may be involved in it, as in 

 cases of hydrophobia, in which the sound or sight of water, operating 

 through the cerebrum, will produce spasmodic convulsions. 



From the facts presented by the lower animals, it may be inferred that 

 the spinal cord does not act as a single organ, but rather should be re- 

 garded as a collection of ganglia, special duties being discharged by spe- 

 cial parts of it. 



With respect to the commissural action of the spinal cord, reference has 

 Connection of a ^ rea ^7 ^ een ma de to the structural connection between the 

 the cord and cord and the nervous regions above it, and in referring to the 

 old anatomical doctrine that each of the spinal nerves is con- 

 nected by continuous fibres with the brain, due weight has been given 

 to the fact that the cord does not increase in thickness as it approaches 

 the brain, but that its bulgings correspond to the regions from which it is 

 necessary that an unusual supply of nerves should be given off. The 

 force of this argument is, however, considerably diminished when we 

 recollect that the nerve-tubes are by no means of uniform diameter, but 

 are doubly conical in shape. Even, therefore, with a diminished diame- 

 ter of the spinal cord, there might be an upward continuation of spinal 

 fibres, the diameter of which is becoming less and less ; and this seems 

 to be rendered more likely from the analogy of the structure of the ven- 

 tral cord of the articulata, in which fibres are sent to the cephalic gan- 

 glia for the purpose of establishing a communication between them and 

 the roots of the nerves. But, however that may be, there can be no 

 question of the influence of the brain over spinal action, and this, of course, 

 implies structural connection of some kind an intercommunication 

 which, if it does not take place solely through the white columns, must 

 take place through the gray material. It is, however, important to ob- 

 serve that the gray material has no direct communication with that of 

 the cerebrum, but, passing through the optic thalamus, ends in the cor- 

 pus striatum, extending therefore in one continued mass through the cord, 

 and terminating in that ganglionic organ. By one or both of these chan- 

 nels, white or gray, the impressions which are made upon the spinal 

 sensitive nerves are presented to the brain, and in a similar manner the 

 influences which produce voluntary motions are transmitted down. A 

 Effect of le sect ^ on ^ an 7 P art ^ tne s P ma l cor< l at once incapacitates the 

 sionsofthe will from acting upon the parts beyond, the motions of which 

 cord< become therefore purely automatic, though the parts above still 



