THE PROPERTIES OF MUSCULAR TISSUE 89 



a very slowly increased pressure, even if ultimately very great, or 

 a very slowly raised temperature, or a slowly increased electrical 

 current passed through it, will not excite the muscle; although far 

 less pressure, warmth, or electricity more rapidly applied would 

 stimulate it powerfully. Once an electric current has been set up 

 through a muscle, its steady passage does not act as a stimulus; 

 but a sudden diminution or increase of it does. It may perhaps 

 still be objected that it is not proved that any of these stimuli ex- 

 cite the muscular fibers, and that in all these cases it is possible 

 that the muscle is only excited through its nerves. For the various 

 stimuli named above also excite nerves (see Chap. X), and when 

 we apply them to the muscle we may really be acting first upon 

 the fine nerve-endings there, and only indirectly and through the 

 mediation of these upon the muscular fibers. That the muscular 

 fibers have a proper irritability of their own, independently of their 

 nerves, is, however, shown by the action of certain drugs for ex- 

 ample curare, a South American Indian arrow poison. When this 

 substance is introduced into a wound all the striped muscles are 

 apparently poisoned, and the animal dies of suffocation because of 

 the cessation of the breathing movements. But the poison does 

 not really act on the muscles themselves: it has been proved to 

 paralyze the very endings of the muscle-nerves right down in the 

 muscle-fibers themselves. Yet after its administration we still 

 find that the various non-physiological stimuli referred to above 

 make the muscles contract as powerfully as before the poisoning, 

 so we must conclude that the muscles themselves are irritable in 

 the absence of all nerve stimuli or, what amounts to the same 

 thing, when all their nerve-fibers have been poisoned. The ex- 

 periment also shows that the contractility of a muscle is a property 

 belonging to itself, and that its contracting force is not something 

 derived from the nerves attached to it. The nerve stimulus simply 

 acts like the electric shock or sudden blow and arouses the muscle 

 to manifest a property which it already possesses. The older 

 physiologists observing that muscular paralysis followed when the 

 nervous connection between a muscle and the brain was inter- 

 rupted, concluded that the nerves gave the muscles the power of 

 contracting. They believed that in the brain there was a great 

 store of a mysterious thing called vital spirits, and that some of this 

 was ejected from the brain along the nerve to the muscle, when the 



