290 THE BODY AT WORK 



and one long process, the ste.ni of the stool. No structure could 

 be more suggestive of the function of the organ ; but no one 

 has as yet succeeded in catching the suggestion and pressing 

 it into a definite explanation of the way in which it works. 

 Certain physiologists, laying great stress on the fact that the 

 functional connections between an electric organ and its nerves 

 are not easily interrupted by the administration of curari, 

 atropin, and other drugs, which block the passage of impulses 

 from nerves to muscles, look upon the nerve-layer of the disc 

 as the generator of electricity, and the rest as an accumulator 

 or resonator, which stores, or exaggerates, the electric charge. 

 Others consider that the portion of the disc which is altered 

 muscle-fibre the middle, or middle and posterior layers 

 generates the electromotive force, the nerve simply calling it 

 into activity. All agree that a brief interval (about 0-003 

 second) elapses between the arrival of the nerve-impulse and 

 the discharge of an electric shock. This " latent period " 

 may be used as an argument in favour of either view. It 

 would be in harmony with the general account which we have 

 already given of protoplasm as a liberator of energy to sup- 

 pose that a nerve-impulse, having reached a disc, immediately 

 infects the protoplasm of the disc, inducing molecular commo- 

 tion, and that the ions move in such directions as to dis- 

 turb the electric equilibrium of the disc, its front surface 

 becoming in relation to the back as zinc to copper in a battery. 

 The current generated in the fish is in the direction from head 

 to tail. It is certain that the change does not occur until an 

 impulse reaches the organ. The organ is not charged by the 

 nervous system during a period of inactivity, and then dis- 

 charged by a releasing impulse. This is sufficiently evident 

 from the fact that when a piece of the organ, with its nerve, is 

 removed from the fish, although much sooner exhausted, it re- 

 sponds like a nerve-muscle preparation to repeated stimulation. 

 The usefulness of a torpedo's electric organs is unmistak- 

 able. They are powerful enough to paralyse every animal 

 that touches its back, whether foe or little fish suitable for 

 food. But of what service is its feeble battery to a skate ? 

 This and the allied question as to the advantages which can 

 have accrued to the ancestors of the torpedo who first began 

 to . change innocent muscle into a weapon of offence are 



