v SPINAL COED AND NEEVES 291 



normal conditions the character of reactions induced by external 

 influences, in the form of movements which are adapted to adjust 

 the organism temporarily to its environment. In a word, the 

 reflex act is the elementary nervous process that underlies the 

 most complex activities of the spinal system. Many of the spinal 

 acts commonly termed automatic or spontaneous, since they appear 

 to be independent of external influences, are classed by other 

 authors among reflex actions, the distinction between reflex and 

 automatic acts having varied at different periods and in different 

 schools. To this we shall return later. 



The first question before entering on the study of the spinal 

 reflexes is to determine whether sensation and movement depend 

 on separate nerve-fibres or not, i.e. are the sensory impulses from 

 the periphery to the cord conducted by the same fibres as those 

 which conduct motor impulses from the cord to the muscles ? 



From remote antiquity it has been assumed that the sensations 

 and the movements of animals depend on distinct nerve-fibres. 

 Herophilus and Erasistratus, as well as Galen, affirmed this from 

 their clinical observations, and from the varying effects of injury, 

 which abolished now sensibility, now motility, and by irritating 

 the former produced pain, or, by exciting the latter, convulsions. 

 " There are nerves," said Galen, " to the muscles and others to the 

 skin : when the former are affected, movement is abolished, when 

 the latter, sensibility." 



The next question is whether the motor and sensory nerves 

 enter and leave the cord together or separately. Starting from 

 the anatomical fact that the spinal nerves emerge by two distinct 

 roots from the cord, Walker (1809) was happily inspired to 

 attribute different functions to these roots. But as he made no 

 experiments he fell into the error of attributing sensation to the 

 ventral, and motor functions to the dorsal roots. In the same 

 year the celebrated naturalist Lamarck hit on the same idea, 

 but did not actually determine the function of either root. The 

 first experimental research in this matter was made by Charles 

 Bell (1811). But as he worked with freshly killed rabbits he 

 was unable to establish the function of the dorsal roots, and 

 merely succeeded in demonstrating the motor nature of the ventral 

 roots. Convincing proof of the different functions of the two roots 

 was not forthcoming for another ten years, when it was afforded 

 by the work of Magendie, Joh. Mitller, Panizza, Longet, and 

 Claude Bernard. 



In 1822 Magendie discovered that cutaneous sensibility is 

 abolished in the regions supplied by the fibres coming from 

 divided dorsal roots, while it is unimpaired when the ventral roots 

 are cut. He exposed the posterior portion of the cord in very 

 young dogs, divided the .lumbar and sacral dorsal roots on one 

 side, and closed up the wound. At first the limb on the operated 



