262 SOME CHAPTERS ON THE 



whether a nervous impulse is passing or not, so that the electrical 

 signs of nerve activity have assumed a greater importance than 

 is the case in the physiology of other organs of the body. Further, 

 these effects, occurring in such a highly specialised structure as 

 nerve, have seemed a suitable object for the attempted explana- 

 tion of many problems of general physiology. It becomes then 

 a. matter of great interest to see how far these electrical effects 

 observed on excised nerve represent the events occurring in nerve 

 still in the body, especially as evidence has been brought forward 

 to show that it may be possible, under exceptional circumstances, 

 to have a nervous impulse without the corresponding electrical 

 change ( 4 ). 



II. NERVES IN THE LIVING ANIMAL 



The first of the modern instances we shall quote is from the 

 work of Gotch and Horsley ( 9 ). In this there is one series of 

 experiments that bear on this question. In the cat and the 

 monkey both the sciatic nerves and the cut end of the spinal cord 

 gave unmistakable evidence of a negative variation which accom- 

 panied the excitation due to the reflex discharges from the 

 nervous centres when these were excited by absinthe or (more 

 markedly) by strychnine. Negative variations produced in this 

 manner corresponded exactly with those produced by the electri- 

 cal excitation of the cortex and other parts, and except in so far 

 as the nerve impulse might be altered centrally by the drug 

 (Sherrington 10 ), these variations represent the results of the 

 normal excitation of the nerve fibre by the nerve cells. 



Bernstein ( u ) in 1898 observed a similar phenomenon. If a 

 pithed frog be lightly strychninised, the muscles of the hind legs 

 fall into tetanus whenever any stimulus reaches the spinal cord. 

 These tetanic contractions are more or less synchronous, and if 

 by a modification of Bernstein's method one of the legs of the 

 frog be connected with a myograph, and the sciatic nerve of the 

 other be placed on electrodes, and connected with a galvanometer 

 or electrometer, it can be easily seen that when there is a con- 

 traction of the muscles there is a negative variation in the sciatic 



lias shown that if strong induction shocks are passed lengthwise through a nerve 

 (or any other moist conductor), that the heating effect of the current produces 

 either lengthening or shortening, according as evaporation or rise of temperature 

 predominate. 



