320 ELECTRO-PHYSIOLOGY CHAP. 



theory, Pfliiger (32) has very acutely tried to establish a view 

 associated, on the one hand, with the idea of a molecular structure 

 of the nervous substance, and illustrating its essential phenomena 

 under the figure of physical alterations within the system, while, 

 on the other, it is in line with all the experimental data known 

 up to the present. We shall mainly refer to the lucid 

 account which Funke (Physiol. 4th ed. i. p. 865 ff.) gives of 

 Pfliiger's theory. Pfliiger starts with the presumption that there 

 is in nerve as, indeed, in all " excitable " substances a combina- 

 tion of molecules " which constantly strives to enter into motion, 

 but cannot, because there is an obstacle, a molecular inhibition. 

 Since the molecular combinations of the system have a constant 

 tendency to movement, there must be a constant force which 

 drives them. But inasmuch as the molecules remain at rest, the 

 force of inhibition must be equal and opposite to the former " 

 (Pfliiger, I.e. p. 478). In the resting condition of the nerve, the 

 two forces of molecular energy and molecular inhibition are in 

 equilibrium, the latter being maintained by given forces at a given 

 position, which it instantly recovers when other forces working 

 upon it have produced a temporary disturbance. Displacement 

 of the elastic molecular inhibition in a double and opposite direction 

 must further be possible, the conditions for discharge of energy 

 being induced by the displacement in one of these directions, in 

 such a way that more potential is converted into dynamic energy 

 in proportion as inhibition is displaced in one direction, while 

 displacement in the opposite direction, on the contrary, produces 

 accumulation of potential energy. 



Pfliiger gives a graphic figure of the mechanism of discharge in 

 any cross-section of the nerve. A cylinder bent at right angles 

 (ABC, Fig. 220) carries on its horizontal limb AB a water-tight 

 piston 1), which is movable in the direction of the arrows ab and 

 cd. A compressed spring fastened to the piston presses against it 

 on one side, and impels it with a certain force in the direction 

 ab. On the other side, the fluid poured into the vertical arm of 

 the cylinder pushes against the piston, with the hydrostatic 

 pressure corresponding with the height of the column of fluid 

 in the vertical lirnb BC, and tends to push the piston in the 

 direction cd. The piston will obviously come to rest in 

 that position at which the tension of the spring, and the pressure 

 of the column of fluid, are in equilibrium. Behind the piston 



