194 HUMAN PHYSIOLOGY 



metabolism by measuring the heat produced in the stimulated 

 muscle. When a tetanized muscle, carrying a load, holds 

 the load suspended, it no longer does any work, hence all 

 the transformed energy appears as heat. 



To conduct the experiment in such a manner that the muscle 

 in acting shall do no external work, the raised weight is left on 

 the muscle, and when the muscle relaxes it is allowed to sink. 

 The heat produced by an excised frog-muscle is measured by the 

 thermo-electric method, a delicate thermopile being used. In 

 many cases the heat produced by a contracting muscle can be 

 directly measured by a delicate thermometer placed upon the skin 

 over the muscle. 



By a single contraction the frog-muscle increases in tem- 

 perature by 0.001 to 0.005 C., during tetanus more. 

 The amount of heat produced by the twitching of a frog- 

 muscle of one gram is about three micro-calories. This 

 amount of heat is produced by the oxidation of 0.0008 mg 

 sugar. 



C. Electrical phenomena in the active muscle. The 

 part of the muscle in contraction is negative to the resting 

 part. The development of electricity during contraction 

 occurs mostly during the latent period, so that the negative 

 phase is nearly past before the contraction begins. The 

 wave of contraction is preceded by a " negative wave." 



Suppose AB in Fig. 1 1 to be a muscle fibre, the points 

 a and b of which are connected with a galvanometer L. If 



FIG. ii. 



we stimulate the muscle at C, immediately after the stimula- 

 tion has reached a an electric current passes through L 

 from b to a, a having become negative. Soon after this, 

 when the stimulation has reached b, the current passes 

 through L from a to b. These currents are called the 

 action-currents and follow each other with great rapidity. 



