ON THE MAMMALIAN NERVOUS SYSTEM. 421 



This being the case, the whole series of experiments are in reality a demonstration 

 of the extent to which one complicated reflex act is influenced by the awakening in 

 the entire nervous system of a whole series of reflex discharges. The uncertainty 

 which must attend such a method may be illustrated by the following experience of 

 ourselves. It often happened in the experiments described in this paper (all of 

 which were performed under an ansesthetic), that after not merely complete section, 

 but absolute removal of a piece of cord 1 centim. long in the mid-dorsal region of the 

 Cat or Monkey, mechanical irritation of the sciatic nerve, and especially of the posterior 

 roots, caused not merely movement in the upper limbs, but of the head, &c., also. 

 This effect was an indication that the anaesthesia had become too slight, and it was 

 immediately abolished on making the latter rather more profound. We convinced 

 ourselves that the mechanism of its causation consisted in first a reflex of the lower 

 limbs, and that this movement dragging on the trunk aroused a reflex in the upper limbs 

 by pulling on the nerves of the upper fragment of cord, which in the neighbourhood 

 of the section was in a hyperexcitable state. The afferent impulses thus started now 

 evoked general movements by discharging the higher centres. The movements of the 

 lower and upper limbs often followed one another so rapidly that the eye was unable to 

 distinguish between their time of commencement ; in some cases, however, particularly 

 when the narcosis was increased, the delay between the two was quite plain, and every 

 stage might be observed. Of what value, therefore, as regards the question of conduc 

 tion in the continuous tracts of fibres in the spinal cord are the results of experiments 

 in which the animal is under no anaesthetic at all, for the employment of curare 

 by MIESCHER did not provide for the adequate exclusion of reflex centres such as can 

 be obtained by the use of ether. Indeed, MIESCHER S method depended upon the 

 maintenance of the functional activity of the reflexes. It seems to us, therefore, that 

 this is the crucial point of the whole position, and accounts for the capricious character 

 of the results of different observers as dependent upon different methods of investi 

 gation. The index for the arrival of nerve impulses from one side of a block in the 

 cord to the other has always been a reflex one, and it is essential lor its proper 

 working that the reflex centres should be in an excitable condition. Since the experi 

 ments involve operating on the cord and the examination of the animal in the 

 unamesthetised state, within a short time of the operation there is every opportunity 

 for abnormal conditions of the other centres (in consequence of the procedure), to 

 influence the result; such influence is so certain from the state of the animal that tiie 

 results really determine, not the localisation of afferent fibres in the cord, but the 

 extent to which the operation has augmented or depressed the excitability of 

 the successive central mechanisms, and the bridge by means of which the lower 

 and upper parts of the cord communicate thus becomes chiefly a column of inter- 

 nuncial fibres. Moreover, almost all experiments done within a few hours of the time 

 of operation lay themselves open to our further criticism, that it is possible for the 

 reflex movement of the hind limbs and trunk to arouse by mechanical pull of the parts 



