ON THE MAMMALIAN NERVOUS SYSTEM. 



465 



described. With a stimulus of 2000, effects in the right sciatic nerve were observed 

 only from excitation of the posterior and lateral columns of the same side, the deflec- 

 tions amounting to an average of 10 only. On increasing the stimulus to a considerable 

 strength (4000) a deflection of 70 was produced by the excitation of the lateral column 

 of the same side. 



Still more striking experiments are the following made upon two animals (Cats), 

 which may be set out in detail, the necessary strength of the stimulus employed being 

 noteworthy. 



EFFECT in Efferent Nerves following Excitation of Spinal Cord. 



In the preceding experiments with afferent fibres, the maximal intensity of the 

 stimulus was that represented by ,2000 ; the great increase in the intensity of the 

 cord stimulus necessary to evoke effects in the nerve through efferent fibres is, there- 

 fore, very striking. 



Another animal (Cat) which was experimented upon in the same way, must be con- 

 sidered as furnishing rather doubtful evidence, since we had previously not only exposed 

 and excited 'the cut ends of the various divided posterior roots on the side of the nerve 

 in order to obtain reflex effects, but had divided all the anterior roots on the opposite 

 side of the cord. These operations must, from their severity and extent, have altered 

 the excitability of the cord itself. As far as they go, however, the results are in 

 accordance with those just set forth, since a stimulus of considerable intensity (3000) 

 was necessary to evoke any effect in the nerve which, in the case of excitation of both 

 posterior columns amounted to 30, and in that of the lateral column of the same side 

 to 36. 



Finally, in order to avoid the changes in excitability following immediate section of 

 the posterior roots, those belonging to the 5th, 6th, 7th lumbar, and 1st sacral nerves, 

 were divided on the left side in a Cat (227) 26 days before the experiment. When 



MDCCCXCI. B. 3 O 



