354 On the Effects of Constant Galvanic Currents. 



In regard to those other conditions, the article, " Eeflex-umkehr " (' Ergebnisse 

 der Physiologie ') by Graham Brown (4), where the cases are exhaustively 

 summed up, may be consulted. 



Gonclusions. 



(1) The "excitation formula" (Pfliiger's law) holds good in mammalian 

 nerve both efferent and afferent. When the threshold value of stimulation is 

 high, as in some decerebrate reflex preparations, the contraction at break of 

 the ascending current takes place in an earlier stage than that at its make, 

 though the reverse is true if the current is descending. 



(2) During the passage of a weak constant galvanic current, no continuous 

 excitation is produced in either nerve muscle or reflex preparation. If a 

 stronger descending current is passed through the nerve, this occurs in both 

 preparations ; though if the current is ascending, this is usually not the case. 

 Far stronger currents are necessary to produce it in the reflex than in the 

 nerve-muscle preparation. 



Two days after division of the sciatic nerve, no continuous excitation is 

 produced during the passage through the nerve of constant current, however 

 strong, either ascending or descending. 



(3) In nerve-muscle preparations, if the nerve is in bad condition after 

 prolonged exposure, it acquires the character of responding more easily, with 

 tetanus at the make of the descending and at break of the ascending current. 

 When the condition is advanced the muscle seems to be in a weak contraction 

 even when no stimulus by the current is being given to it: the passage 

 through it of an ascending current then causes a relaxation of the muscle 

 during the passing of the current. 



(4) As to the relation between reflex excitation and reflex inhibition the 

 following can be stated : — 



The intensity of the inhibitory and excitatory reflex effects on the tonus of 

 the vasto-crureus muscle and the relation between these two effects are 

 determined by the strength, duration and direction of the stimulating current, 

 but are also influenced by the degree of tonus in the preparation, the initial 

 length of the muscle, and the position of the neck and other joints. Any 

 condition which favours the tonus of the extensor muscle causes increase in 

 the excitatory tendency of the reflex effect and diminution in the inhibitory 

 tendency, and vice versd. The reversal of reflex effect is thus often obtained 

 by altering these conditions without changing those of stimulation. 



I am greatly indebted to Prof. C. S. Sherrington for suggestions and advice 

 during the course of these experiments. 



