262 PHYSIOLOGY CHAP. 



inents, which contradicted those of Wundt, who had previously 

 found a delay of 0'02 sec., were repeated by Moore and Eeynolds 

 (1898) at Schafer's instigation. They cut all the bundles of a dorsal 

 spinal root in the frog, except one, and recorded the reflex time of 

 a muscular contraction on exciting first the remaining bundle of 

 the root and then the nerve before its entrance into the ganglion. 

 They found that the latent period did not vary perceptibly, which 

 led them to conclude that the afferent excitations traversing the 

 sensory paths do not pass through the body of the ganglion cells, 

 the true function of which is trophic. 



But can this conclusion from the spinal ganglion cells be 

 properly extended to all ganglion cells of the grey matter of the 

 central nervous system of vertebrates ? Can we from the physio- 

 logical standpoint unreservedly accept the theory of Apathy and 

 Bethe that the diffuse network of nerve fibrils, which appears to 

 be the universal and essential medium of the reciprocal relations 

 between the different fibres and the ganglion cells, represents the 

 true and only substrate of the central neural phenomena ? 



Possibly our knowledge is not yet enough advanced to be able 

 to give a decisive and final reply to this question. But it is closely 

 related to the question of the specific energies called out by the 

 excitation of the different sensory nerves. What is the true 

 material basis of specific energy ? Why does the optic nerve in- 

 variably respond by visual sensations and the auditory nerve by 

 sensations of sound, whatever the nature of the stimulus that 

 affects them ? Does this depend on the specific nature of the 

 neurones in toto, i.e. on the peripheral conducting paths as well as 

 the centres ; or are all conducting nerve-fibres essentially identical 

 in character, and is the substrate of specific energy represented by 

 the peripheral and central, sensory and motor connections of the 

 nerves ? Most physiologists, particularly those who have studied 

 the general physiology of nerve (among them Du Bois-Reymond 

 and Hermann) are in favour of the latter view. 



Still there are not wanting supporters of the opposite theory, 

 who assign to the individual fibres (sensory and motor, medullated 

 and non-medullated) a qualitatively different functional nature 

 (Griitzner and others). Hering (1899), on the strength more 

 particularly of his studies on the physiology of the senses, declared 

 emphatically against the doctrine of the identity of nerve functions, 

 and assumed instead that the individual neurones differed not only 

 by their different place in the system, but also by the qualitatively 

 different nature, innate or hereditary, of their activity. 



Whatever the final solution of this difficult problem, it is 

 certain that the mode in which the central grey matter reacts 

 to direct or indirect stimulation presents certain characteristic 

 peculiarities by which it is distinguished from the peripheral 

 nerves. 



