HEAT PRODUCED IN A SIMPLE CONTRACTION 



483 



in all probability due to chemical changes going on in the muscles at the in- 

 jured ends. 



Action Currents. When a muscle is made to contract the demar- 

 cation current undergoes a sharp decrease, as shown by the deflection of the 

 galvanometer needle, which swings back in the direction of equilibrium. 

 This deflection, originally called the current of negative variation, has been 

 shown to be due to the processes going on in the muscle during contraction, 

 and is therefore more properly called the action current. It occurs where no 

 previous demarcation current exists. 



For the study of the action current the capillary electrometer is very con- 

 venient. The hearts of cold-blooded animals, because of their slow con- 

 traction, serve well for demonstration. The muscle contraction passes over 



FIG. 324. Diagram of the Currents in a Muscle Prism. (Du Bois Reymond.) 



the ventricle in the form of a wave, the electric potential of the muscle chang- 

 ing as it becomes active or passive. For any two points on the heart muscle, 

 therefore, there will be two changes of potential, the active part first becom- 

 ing negative to the inactive, and then, as the wave passes down and the in- 

 active part becomes active, the current is reversed. This is known as a 

 diphasic current. 



In certain fishes definite electrical organs exist, organs which are derived 

 from muscle-like tissues and which may be regarded morphologically as mus- 

 cles highly specialized for the production of energy in the form of electricity. 



Heat Produced in a Simple Contraction. Becquerel and Breschet 

 found, with the thermo-multiplier, about 0.5 C. of heat produced by each 

 forcible contraction of a man's biceps; and when the actions were long con- 

 tinued, the temperature of the muscle increased i C. In the frog's muscle 

 a considerable number of contractions have been found to produce an ele- 

 vation of temperature equal on an average to less than o. 2 C., while a single 

 contraction produces, according to R. Heidenhain, from 0.001 to 0.005 C. 

 One gram of frog's muscle will produce in a single maximal contraction about 

 0.003 calorie or the equivalent of 128 gramcentimeters of work energy (since 



