THE PHENOMENON OF CONTRACTION. 35 



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 Heiclenhain, 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. Second. 

 Some electrical energy is developed during the contraction. The 

 means of detecting and measuring this energy will be described 

 in a subsequent chapter. Considered quantitatively, the amount 

 is small. Third. Work is done if the muscle is allowed to shorten 

 during the contraction. By work is meant external or useful 

 work that is, the muscle lifts a weight or overcomes an opposing 

 resistance. If a muscle contracts against a weight too heavy 

 to be lifted or a resistance too strong to be overcome it does no 

 external work, although, of course, much energy is liberated as 

 heat or, as it is sometimes called, internal work. The work done 

 by a muscle during contraction is measured in the usual mechanical 

 units, by the product of the load into the lift. That is, if a muscle 

 lifts a weight of 40 grams to a height of 10 millimeters, the work 

 done is 40 X 10 = 400 gram-millimeters, or 0.4 grammeter. We 

 can in calculations convert external work into heat or internal 

 work by making use of the ascertained mechanical equivalent of 

 heat, according to which 1 calorie -= 425 grammeters of work. 

 The work, 0.4 grammeter, supposed to be done in the above experi- 

 ment would be equivalent, therefore, to 0.4 ~ 425, or about 0.001 

 of a calorie. 



