THE PHENOMENON OF CONTRACTION. 23 



We know now that in the course of several days the severed nerve 

 fibers degenerate completely down to their terminations in the 

 muscle fibers, and the muscle, thus freed from its nerve fibers by 

 the process of degeneration, can still be made to contract by an 

 artificial stimulus. The classical proof of the independent irri- 

 tability of muscle fibers was given by Claude Bernard, the great 

 French physiologist of the nineteenth century. He made use 

 of the so-called arrow poison of the South American Indians. 

 This substance or mixture o. substances is known generally under 

 the name curare; it is prepared from the juices of several plants 

 (strychnos) (Thorpe). The poisonous part of the material is soluble 

 in water, and Bernard showed that when such an extract is injected 

 into the blood or hypodermically it paralyzes the motor nerves 

 at their peripheral end, so that direct stimulation of these nerves 



Fig. 6. The induction coil as used for physiological purposes (du Bois-Reymond 

 pattern): A, The primary coil; B, the secondary coil; P', binding posts to which are at- 

 tached the wires from the battery, they connect with the ends of coil A : P", binding posts 

 connecting with ends of coil B, through which the induction current is led off; S, the slide, 

 with scale, in which coil B is moved to alter its distance from A. 



is ineffective. Direct stimulation of the muscle substance, on the 

 contrary, causes a contraction.* 



Artificial Stimuli. If we designate the stimulus that the 

 muscle receives normally from its nerve as its normal stimulus, 

 all other forms of energy which may be used to start its contraction 

 may be grouped under the designation artificial stimuli. Experi- 

 ments have shown that a contraction may be aroused by mechanical 

 stimuli, for instance, by a sharp blow applied to the muscle; by 

 thermal stimuli, that is, by a sudden change in temperature; by 

 chemical stimuli, for example, by the action of concentrated solu- 

 tions of salts, and finally by electrical stimuli. In practice, however, 

 only the last form of stimulus is found to be convenient. The 

 mechanical and thermal stimuli cannot be well applied without at 

 the same time injuring the muscle substance, and the same is prob- 

 ably true of chemical stimuli, which possess the disadvantage, more- 

 over, of not exciting simultaneously the different fibers of which the 



* 'Lecons sur les effets des substances toxiques et medicamenteuses/' 

 1857, pp. 238 et seq. 



