72 THE PHYSIOLOGY OF MUSCLE AND NERVE. 



Fig. 27. — Engelmann's artificial muscle. The artificial muscle is represented by the cat- 

 gut string, m. This is surrounded by a coil of platinum wire, w, through which an electrical 

 current may be sent. The catgut is attached to a lever, h, whose fulcrum is at c. The catgut 

 is immersed in a beaker of water at 50° to 55° C, and "stimulated " by the sudden increase 

 in temperature caused by the passage of a current through the coil. — (After Engelmann.) 



Fig. 28. — Curve of simple contraction obtained from an artificial muscle. The dura- 

 tion of the stimulus (heating effect caused by the current) is shown by the break in the 

 line beneath the curve. 



muscle cannot work as a heat engine by transforming a part of -the heat of the 

 chemical reaction to work. A difference in temperature is necessary that is 

 not possible in the case of muscle. More recent speculations have assumed 



