248 VETERINARY PHYSIOLOGY 



ture of 15 "05^ C, after a period of contraction, then Oo 

 gram- degrees of heat have been produced ; i.e. heat sufficient 

 to raise the temperature of 0*5 gram of water through 1° C. 



The amount of energy liberated as heat may be cal- 

 culated by the various methods considered in studying 

 metabolism (p. 259). 



The heat units employed are the small and large calories — 

 the small calorie, the heat required to raise one gram of 

 water through one degree Centigrade, and the large Calorie — 

 generally written with a large C — the heat required to raise 

 a kilogram of water through one degree Centigrade. 



8. The Relationship of Work Production to Heat 



Production. 



The Mechanical Eflaciency of Muscle. 



The proportion of work to heat is not constant in muscle 

 any more than it is in an engine. If an unloaded muscle is 

 made to contract, no work is done and all the energy is 

 given off as heat, and the same thing happens when, in 

 isometric contraction, a muscle is so loaded that it cannot 

 contract when stimulated. 



Since it is possible to measure the tension exercised upon 

 a spring in isometric contraction and to measure the amount 

 of heat produced, and since in such a contraction all the 

 energy is finally given off as heat, it is possible to calculate 

 the proportion between these. The efficiency in such con- 

 ditions is found to be nearly 100 per cent. ; but this is no 

 measure of the actual efficiency of the muscles. 



The point of practical importance to decide is — How 

 much of the energy liberated by muscle hi normal 

 conditions is available under favourable circumstances for 

 mechanical work, and how much is lost as heat ? 



To determine this, the way in which muscle develops 

 tension when stimulated must be studied. 



The Development of Tension by Muscle. 

 It has for long been recognised that muscle like other 

 protoplasm gets its energy f]?om food. But the problem 



