THE ACTIVITIES OF THE ORGANISM 103 



with the element (2). The condition in (2) is fl,„ + &^ = 

 Cp + d,, and that of (i) a„^v + h„i^Cpi + d,x, but these 

 two together now fall into a new state of equilibrium 

 and this is transmitted along the whole nerve-fibril 

 with a velocity which belongs to the order of magni- 

 tude of that of chemical changes. If the stimulus 

 remains constant (a constant electric current for in- 

 stance), the new condition of equilibrium will be 

 established throughout the whole length of the fibril 

 and the nervous impulse will be a momentary one 

 (as it is in this case). But if the stimulus is an inter- 

 mittent one (an interrupted electric current, light- 

 vibration, sound- vibrations), then in the intervals the 

 former condition of equilibrium will become re-estab- 

 lished and the nervous impulse will be intermittent 

 (as it is). There would be no work done on the whole 

 in the changes, except that done by the transmission 

 of the changed state of equilibrium to the substance 

 of the effector organ in which the nerve-fibril terminates 

 — the substance of a muscle fibre, or the cell of a 

 secretory gland, for instances. There would, prob- 

 ably, be a certain dissipation of energy as in the case 

 of the propagation of an electric impulse through a 

 poor conductor, but all our knowledge of the chemistry 

 of the nerve fibre points to this amount of dissipation 

 as tending to vanish. 



Something analogous to this may be expected to 

 take place in a muscle fibre when it contracts ; except 

 that, of course, energy is transformed in this case. 

 What precisely does happen we do not know and at 

 the present time no physico-chemical hypothesis of 

 the nature of muscular contraction exactly describes 

 all that can be observed to take place. Certain 

 positive results have, of course, been obtained by 

 chemical and physical investigation of the contracting 



