484 



MUSCLE-NERVE PHYSIOLOGY 



i calorie = o . 4267 kilogrammeter of work) . The cause of the rise of tempera- 

 ture is the increased chemical activity at the time of contraction. As we 

 have already seen, in the chapter on Animal Heat, muscles have the power of 

 producing heat even when not contracting, i.e., changing shape. 



The amount of heat energy developed during a single contraction will 

 vary sharply according to the tension under which the muscle contracts. 

 The heat production follows closely the energy of work produced, and 

 apparently obeys the same laws. 



FIG. 325. Figure for Work Energy, Showing Height of the Contraction of the Gastroc- 

 nemius of the Frog with Loads Increased by Ten Grams at a Time. 



The Work Energy Liberated by a Simple Muscle Contraction. 



When a muscle contracts against a resistance and a load is moved, work 

 energy is liberated. In fact, the liberation of work energy and heat energy 

 are the specific functions of the muscles among the warm-blooded animals. 

 A frog's gastrocnemius weighing i gram and loaded with 50 grams will 

 contract from 0.5 to 0.6 cm.; i.e., will do 25 to 30 gramcentimeters of work 

 for each simple contraction. The amount of work done is intimately associ- 



TABLE SHOWING THE RELATION BETWEEN LOAD AND WORK. 



