THE PHENOMENON OF CONTRACTION. 37 



Idiomuscular Contractions. In a fatigued or moribund muscle mechan- 

 ical stimulation may give a localized contraction which does not spread or 

 spreads very slowly, showing that the abnormal changes in the muscle prevent 

 the excitation from traveling at its normal velocity. A localized contraction 

 of this kind was designated by Schiff as an idiomuscular contraction. It may 

 be produced in the muscle of a dying or recently dead animal by localized 

 mechanical stimulation, as by drawing a blunt instrument e. g., the handle 

 of a scalpel across the belly of the muscle. The point thus stimulated stands 

 out as a wheal, owing to the idiomuscular contraction. 



The Energy Liberated in the Contraction. When a muscle 

 contracts, energy is, as we say, liberated in several forms, and 

 can be measured quantitatively. First, there is a production of 

 heat, which is indicated by a rise in temperature of the muscle.* 

 According to Heidenhain, the temperature of the frog's muscle 

 is increased in a single contraction by 0.001 C. to 0.005 C. Larger 

 muscles, such as those of the thigh of the dog, when repeatedly 

 stimulated may cause a rise of temperature of from 1 to 2 C. 

 The thermometer does not, of course, measure the amount of heat 

 produced, but only the temperature of the muscle. Heat is esti- 

 mated quantitatively in terms of calories. By a calorie is meant 

 the quantity of heat necessary to raise 1 gm. of water 1 C. 

 Knowing the specific heat and weight of muscle, we can readily 

 calculate the number of calories produced. Thus, if a frog's 

 muscle weighing 2 gms. shows a rise of temperature of 0.005 C. 

 from a single contraction the production of heat in calories is given 

 by multiplying the weight of the muscle by its specific heat, 

 0.83, to reduce it to an equivalent weight of water, and this 

 product by the rise in temperature: 2 X 0.83 X 0.005 = 0.0083 

 calorie. The fact that muscular exercise increases the produc- 

 tion of heat in the body is a matter of general observation. Making 

 use of a very sensitive thermo-couple, Hillt has been able to 

 register the production of heat in an excised frog's muscle. In the 

 case of a simple contraction or twitch, the production of the heat 

 is practically instantaneous, indicating an underlying chemical 

 change of explosive suddenness. Analyses of the galvanometric 

 records obtained in these experiments show that there is also a 

 delayed heat production which occurs after the contraction is 

 over. We may say, in fact, that the result of a stimulus causing a 

 contraction is to set up two processes, each of which leads to the 

 development of heat. The heat produced in the first process is 

 detectible during the contraction, while that caused by the second 

 process is subsequent to the act of shortening and, therefore, is. 

 not directly connected with the changes leading to contraction. 

 The significance of this delayed heat production will be referred to> 

 in connection with the chemical changes of contraction and the 



* For general discussion, see Tigerstedt in Winterstein's "Handbuch cL 

 vergleich. Physiologic." 



t Hill, "Journal of Physiology," 40, 389, 1910; 46, 28, 1913. 



