46 HUMAN PHYSIOLOGY 



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 endings in the muscle, stimulation of the nerve 

 still causes muscular contraction. Only when the curare is 

 allowed to act upon the muscle and the nerve endings in the 

 muscle^ does stimulation of tEe~nerve fail to produce any re- 

 action in the muscle, while direct stimulation of the muscle 



causes it to contract. This 

 clearly shows that it is the 

 nerve endings which are poi- 

 soned by _jzygdre, and that 

 therefore the application of 

 stimuli to the muscle must 



FIG. 16. Curare Experiment to show , j. ,1 x , , 



sciatic nerves exposed to curare, ^Ct directly Upon the muscular 



but nerve endings protected on the fibres (Fig. 16). (Practical 



left side; while on the right side p^flfc Chap< IV<) 

 the curare is allowed to reach the y &*' 



nerve endings in the muscle. 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. 



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, Chap. II.) 



2nd. A sudden mechanical change such as may be pro- 

 duced by pinching, tearing, or striking the muscle will cause 

 it to contract. (Practical Physiology, Chap. II.) 



3rd. Any sudden change of temperature, either heating or 

 cooling, stimulates muscle. A slow change of temperature 

 has little or no effect. Every muscle, however, passes into a 

 state of contraction heat stiffening when a sufficiently high 

 temperature to coagulate its proteid constituents is reached. 



