70 THE PHYSIOLOGY OF MUSCLE AND NERVE. 



particles is to make them imbibe the surrounding water. If we 

 further suppose that these particles in the resting muscle are linear 

 or prismatic in shape, then upon imbibing water they will tend 

 to become spherical, causing thus a shortening in the long diameter 

 and an increase in the cross diameter. The muscle, in other words, 

 is an apparatus comparable, let us say, to a gas engine: each 

 stimulus, like a spark, causes the physiological oxidation of a portion 

 of the usable material in the muscle, and the heat thus produced 

 acts upon the doubly refractive material as upon a piece of machin- 

 ery and causes it to shorten by imbibition. Contraction, in a word, 



Fig. 27. 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. 



is a phenomenon of thermic imbibition. Engelmann has given an 

 appearance of verisimilitude to this hypothesis by constructing 

 an artificial muscle from a piece of violin string. The apparatus 

 used is illustrated in Fig. 26. A catgut string (m) is surrounded 

 by a coil of platinum wire (w) through which an electrical current 

 may be sent. The object of this arrangement is to heat the catgut 

 suddenly. The platinum coil should not actually touch the catgut. 

 The catgut is attached to a lever, as shown in the figure. The 

 catgut is thoroughly soaked by immersing it in a beaker of water 

 and the temperature is then raised to 50 to 55 C. If then a 

 current is turned into the coil the slight but somewhat rapid heating 



