162 F. H. SCOTT, 



and still be effective. The ineffectiveness of the cut dorsal roots is due 

 to changes in their nerve fibres or nerve endings, but there is reason to 

 believe the roots are still capable of conducting impulses (cp. pages 150 

 and 161). 



It has been shown also that if the spinal ganglion be left in con- 

 nection with the root recovery of function always occurs after rest. This 

 is true even if its own blood supply be cut off from the ganglion and 

 nourishment supplied only by moistening with diluted blood. 



If a nerve is stimulated peripherally to its spinal ganglion, changes 

 occur in the cells of the spinal ganglion (as described by Hodge and 

 others) if the posterior root is allowed to stimulate the cells in the spinal 

 cord, but no changes occur in such spinal ganglion cells if the dorsal 

 roots are cut before stimulation (also observed by Steinach). 



Some experiments similar to those on the dorsal roots were made 

 with the sciatic nerve, the nerve being cut on one side and left in 

 connection with its nerve cells on the other. Each nerve was stimulated 

 approximately equally for 1^ 2 hours a day. After three or four days 

 the cut sciatic gave much weaker contractions than the intact nerve 

 but complete ineffectiveness was not obtained before the death of the 

 animal. 



Some observations on the form and duration of the crossed reflex, 

 which bear slightly on the questions discussed in this paper, are also 

 given (cp. sect. 6). 



The facts given above seem to me difficult to explain on the common 

 view that the ineffectiveness of a nerve on protracted stimulation (so far 

 as it is not due to fatigue in the cells of the activated organ) is due to 

 abolition of the conductivity of the nerve ending. And it seems to me 

 simpler to suppose that the nerve cells secrete a substance the passage 

 of which from the nerve endings is necessary to stimulation. The 

 recovery of effect after transient fatigue I attribute to the passage of a 

 portion of this substance down the nerve fibre to the nerve ending. 

 The absence of recovery after prolonged stimulation I attribute to the 

 whole of the substance in the nerve fibres being used up, and to their 

 being incapable of making more when severed from their nerve cells. 



Before concluding I take this opportunity of thanking Prof. Munk 

 and especially Prof. Starling for their kindly advice as well as the use 

 of their laboratories and instruments, and also to Prof. Langley for 

 suggestions and help in the publication of this paper. 



