THE TISSUES 43 



action must be had recourse to. If curare, a South American 

 arrow poison, be injected into an animal e.g. into a frog, the 

 brain of which has been destroyed it soon loses the power of 

 moving. When the nerve to a muscle is stimulated, the muscle 

 no longer contracts. But, if the muscle be directly stimulated by 

 any of the various agents to be afterwards mentioned, it at once 

 contracts. 



It might be urged that the curare leaves unpoisoned the 

 endings of the nerve in the muscle, and that it is by the 

 stimulation of these that the muscle is made to contract. But 

 that these are poisoned is shown 

 by the fact that if the artery to 

 the leg be tied just as it enters 

 the muscle, so that the poison 

 acts upon the whole length of 



the nerve except the nerve end- 



,1 i ,. , ,. FIG. 16. Curare Experiment to show 



ings in the muscle, stimulation sciatic nerves ex posed to curare, but 



of the nerve Still Causes niUSCU- ner ve endings protected on the left 



lar contraction. Only when the side ; while on the right side the 

 curare is allowed to act upon the cur f re is all wed t 1 reach the nerve 



, . . endings in the muscle. 



nerve endings in the muscle does 



stimulation of the nerve fail to produce any reaction in the 

 muscle, while direct stimulation of the muscle causes it to con- 

 tract. This clearly shows that it is the nerve endings which 

 are poisoned by curare, and that therefore the application of 

 stimuli to the muscle must act directly upon the muscular 

 fibres (fig. 16). {Practical Physiology} 



Muscle, however, is more readily stimulated through its 

 nerves, and a knowledge of the points of entrance of the nerves 

 into muscles, the motor points, is of importance in medicine 

 in indicating the best points at which to apply electrical 

 stimulation (fig. 17). 



Various means may be used to make the muscle contract. 



1st. Various chemical substances when applied to a muscle 

 make it contract before killing it, while others kill it at once. 

 Among the former may be mentioned dilute mineral acids and 

 metallic salts. (Practical Physiology. ) 



2nd. A sudden mechanical change such as may be produced 

 by pinching, tearing, or striking the muscle will cause it to 

 contract. (Practical Physiology.} 



