THE PROPERTIES OF MUSCULAR TISSUE. 129 



chemical stimuli. One condition of the efficacy of each. of 

 them is that it shall act with some suddenness; a very slowly 

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

 slowly raised temperature, or a slowly increased electrical cur- 

 rent 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 excite the muscular fibres, 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. XIII), 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 fibres. That the mus- 

 cular fibres have a proper irritability of their own, independ- 

 ently of their nerves, is, however, shown by the action of cer- 

 tain drugs for example 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 kills the muscle-nerves, but leaves 

 the muscle intact; and it has been proved to kill the very 

 endings of the muscle-nerves right down in the muscle-fibres 

 themselves. Yet after its administration we still find that 

 the various non-physiological stimuli referred to alove make 

 the muscles contract just as powerfully as before the poison- 

 ing, 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-fibres have been poi- 

 soned. The experiment also shows that the contractility of a 

 muscle is a property belonging to itself, and that its contract- 

 ing 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 interrupted, concluded 

 that the nerves gave the muscles the power of contracting, 



