THE PHENOMENON OF CONTRACTION. 35 



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, of course, a matter of general obser- 

 vation. 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-milli- 

 meters, or 0.4 gramme ter. We can in calculations convert ex- 

 ternal work into heat or internal work by making use of the ascer- 

 tained 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 experiment would be equivalent, there- 

 fore, to 0.4 -*- 425, or about 0.001 of a calorie. 



The Proportion of the Total Energy Liberated that may 

 be Utilized in Work. All of the energy liberated in the muscle 

 has its origin in the chemical changes that follow upon stimulation. 

 We assume that these changes are such that complex molecules 

 are broken down, with the formation of simpler ones, and that 

 some of the so-called chemical or internal energy that holds together 

 the atoms in the complex molecule is liberated and takes the three 

 forms described above. It is a matter of interest to inquire as 

 to the proportion of this total energy which may be converted 

 into useful work and the conditions under which this optimum 

 amount of work may be realized. Regarded from this standpoint, 

 the muscle may be considered as a piece of machinery comparable, 

 let us say, to a gas engine. In the latter the heat generated by 

 the explosive chemical change is converted partially into external 



