82 ELECTRO-PHYSIOLOGY CHAP. 



blood-pressure. From this he inferred the direct excitability 

 of the " sesthesodic " elements of the cord, which, according to 

 Miescher's experiments, are situated chiefly in the lateral columns. 



Schiff disputes the validity of this experiment, and more 

 particularly denies that the centripetal fibres of the lateral columns, 

 from which the reflex is discharged, can be termed " sensory " in 

 the true meaning of the word. This, however, is a by-point in the 

 present connection, where the main object is the determination of 

 direct excitability. How far Schiff's later objections (in which he 

 refers the results of Dittmar's experiments entirely to spread 

 of current to the posterior columns, that are alone excitable) can 

 be justified, must provisionally be left undecided. 



The direct excitability of the motor elements of the spinal 

 cord has, on the other hand, been firmly established. Pick's early 

 experiments above referred to, which were essentially founded on 

 the first of Van Deen's, are open to the objection that the move- 

 ments of the posterior limbs that appear when the ventral half 

 of the frog's spinal cord deprived of its posterior columns 

 is electrically excited, may be due to reflex or direct excita- 

 tion of the fibres of the motor root since there might be 

 spread of current to the uninjured inferior portion of the spinal 

 medulla. Nor is this objection completely removed by the 

 fact that on dividing the ventral half of the cord immediately 

 above the lumbar swelling, and laying the edges together again 

 as closely as possible, the excitatory effect in question fails to 

 make its appearance. On the other hand, the experiment of Van 

 Deen and Fick is fully convincing, under the presumption that 

 motor fibres run longitudinally -in the ventral portion of the 

 spinal medulla, and that their physiological properties coincide in 

 all essential points with those of the peripheral nerve-fibres. And 

 since there is no doubt (infra) that the excitability of peripheral 

 nerves is considerably greater in the immediate proximity of a 

 fresh section than along the continuity of the nerve, it is to be 

 expected, if the motor fibres of the cord give a similar reac- 

 tion, that electrical excitation will take effect at the cut end of 

 the isolated ventral half of the cord sooner, i.e. with less in- 

 tensity of current, than at a lower point, where seeing the 

 closer proximity of the roots of the sciatic the danger of 

 direct excitation by current diffusion is proportionately greater. 

 Biedermaim (37) found, as regards excitability to tetanising in- 



