v SPINAL COED AND NERVES 297 



Von Bezold and Uspensky contested Cyon's results, since they 

 were unable to verify any constant influence of the dorsal upon 

 the ventral roots. According to these authors, the fact recorded 

 by Cyon is rarely met with ; in the majority of cases excitability 

 remains unaltered ; sometimes, indeed, it is temporarily increased. 



This last feature was constantly observed by Marcacci in 

 Dastre's laboratory. He divided all the spinal roots in the frog 

 with the exception of one pair. On then cutting the dorsal root 

 of this pair he found that an induced current that was previously 

 inadequate to evoke a response now threw the muscles innervated 

 by the remaining ventral root into contraction. 



Belmondo and Oddi (1890), under our direction, resumed the 

 experimental study of this subject on the dog. They abolished 

 the influence of the dorsal root, not only by section, but also by 

 the local application of cocaine, which produces temporary paralysis 

 without excitation. Under these conditions they constantly found 

 a marked depression of excitability in the corresponding ventral 

 root, which no longer reacted to the minimal stimuli that had 

 previously been effective. 



In a new series of experiments (1896) Polimanti returned to 

 this subject, and sought to determine the influence exercised on a 

 ventral root, both by the dorsal roots of the same pair and by 

 those of other pairs (above or below) on the same or the opposite 

 side. Generally speaking, he confirmed and extended the results 

 of Belmondo and Oddi, and found that on dividing the dorsal 

 roots there is constantly a marked depression of excitability in 

 the corresponding ventral root. The same result was often 

 obtained on testing the reciprocal influence of two roots of 

 different spinal pairs, on the same or the opposite side. But there 

 was a marked difference between the results of Belmondo and 

 Oddi and those of Polimanti as regards the effects of mechanical 

 or electrical stimulation of the divided dorsal roots. The first 

 authors found that on stimulation of the dorsal roots the excita- 

 bility of the ventral roots was almost invariably increased above 

 the normal ; Polimanti in most cases obtained the opposite result, 

 i.e. depression of excitability, which he held to be a reflex inhibition, 

 probably caused by the excessive strength of the stimulus. But 

 he did not deny that under normal conditions a slow and quiet 

 wave of excitation passes, as assumed by Cyon, from the dorsal to 

 the ventral root, by which its excitability is maintained and on 

 which the tone of the skeletal muscles depends. 



In proof of the reinforcing action of the dorsal upon the 

 ventral roots, it is only necessary to study the motor effects of 

 dividing the former. If one dorsal root alone is divided no very 

 obvious effects ensue, because the influence of adjacent roots 

 readily compensates the functional deficiency. But if several 

 sensory roots are cut, e.g. all those which supply the sensory 



