GENERAL PHYSIOLOGY OF MUSCLE 



63 



cancelled by the negative work of lowering it, so that in this case 

 the heat production in static contraction is equal to that in dynamic 

 contraction. 



But apart from the imperfections of the method Beclard's 

 results were incomplete. He neglected the influence exerted by 

 differences of load on muscular thermogenesis, as well as the degree 

 of stimulation and the state of fatigue of the muscles. In 1864 

 Heidenhain investigated the question again from a wider point of 

 view and by more exact methods. He employed the isolated 

 muscles of the frog, with different loads, and recorded the height 

 of the contractions, from which he calculated the work, and 

 measured the changes of temperature with a thermo-electric pile. 



Since we know that with increase of load the mechanical work 

 of the muscle increases within certain limits (.Fig. 26, p. 46) it 

 seems natural to suppose that the simultaneous development of 

 heat takes place inversely and diminishes with increment of work, 

 so that the sum of energy liberated by the katabolic processes in 

 the muscle remains constant for the same stimulus, its division 

 into work and heat alone being variable. Heidenhain's researches, 

 however, demonstrated that when the intensity of the stimulus 

 remains constant, the sum of energy developed by the muscle 

 increases up to a certain point with increase of load, i.e. the 

 increase of work is accompanied by increased heat-production. 



This important conclusion is represented by the following 

 table, which gives Heidenhain's data from one of his experiments 

 on the gastrocnemius of the frog loaded with different weights : 



During three successive contractions the muscle was loaded 

 with the weight during both contraction and relaxation ; thus the 

 mechanical work given out by the muscle during contraction was 

 restored to it in the form of heat during relaxation. The rise of 

 temperature shown in the table therefore expresses the total sum 

 of the energy developed by the muscle during the three successive 

 contractions. This is not a constant but varies with the external 

 mechanical work : it increases with the increment of this work 



