vin CONDUCTIVITY AXD EXCITABILITY OF NERVE 81 



of 56 cm., when the careful application of electrical, as well as 

 chemical, or mechanical stimuli (pricking, squeezing with forceps) 

 to the segment of cord under observation failed to produce any 

 muscular movement, or sign of painful sensation. 



The conclusion drawn by Schiff from this experiment, to 

 the effect that "in such an animal the (painful) sensations 

 conducted through the spinal cord which has been deprived of 

 its posterior columns cannot be excited by artificial stimulation 

 of the cord itself, and that motor excitability is also wanting in the 

 latter, although it is fully able to transmit a motor impulse," was 

 under these conditions very natural. It proved, however, im- 

 possible to excite the entire uninjured spinal cord of a warm- 

 blooded animal without effect, even after the most careful 

 removal of the posterior roots, since (according to Schiff's view) 

 the irradiating fibres of the sensory roots " still invest the 

 posterior column with a marked degree of sensibility, which 

 is transmitted farther, and results partly in painful sensations, 

 partly in reflexes of various kinds, at different levels of the 

 spinal medulla." Schiff, moreover, differs from Van Deen in 

 ascribing excitability to the nerve-fibres which run ceutripetally 

 along the posterior columns. Excitation of these never produces 

 pain, but causes exclusively tactile sensations, or "kindred sensa- 

 tions of less intensity," betrayed chiefly by alterations in the size 

 of the pupil on electrical or mechanical stimulation of the mostly 

 isolated posterior columns. 



Without entering into details of the numerous attempts to 

 decide the pros and cons of the Van Deen-Schiff theory, we may 

 state that on the one hand Fick (37), followed by Luchsinger, 

 brought forward experiments which determined the existence 

 of directly excitable motor elements in the anterior (ventral) 

 section of the frog's spinal cord, while on the other a series of 

 communications from Ludwig's laboratory asserted the excita- 

 bility of centripetal fibres running in the lateral columns. 

 It is known that the excitation of sensory nerves frequently 

 produces a considerable rise of blood -pressure, owing to in- 

 creased resistance in the arteries from the reflex constriction 

 of numerous vessels. Dittmar (o7) showed that both electrical 

 and weak mechanical excitation of the central end of the rabbit's 

 spinal cord, that has been deprived of its posterior columns for 

 some considerable distance, produces the same marked rise of 



VOL. II G 



