THE TISSUES 6r 



as to increase the speed of a ship or an engine requires an 

 increase of coal consumption in a proportion roughly correspond- 

 ing to the square of the increased speed. 



V. Heat Production in Muscle 



In muscle, as in other machines, by no means the whole 

 of the energy rendered kinetic is used for the production of 

 mechanical work. In a steam-engine much of the energy is 

 dissipated as heat, and the same loss occurs in muscle. 



If heat is given off when a muscle contracts, either the 

 muscle itself, or the blood coming from it, will become 

 warmer. Hence to detect such a charge some delicate method 

 of measuring changes of temperature must be employed. 

 The mercurial thermometer is hardly sufficiently sensitive, 

 and, therefore, the thermo-electrical method is most generally 

 employed. Various forms of thermopile may be used. 



The rise of temperature in a muscle after a single con- 

 traction is extremely small, but after a tetanic contraction, 

 lasting for two or three minutes, it is very much greater. 



The amount of heat produced may be calculated if (a) the 

 weight of the muscle ; (6) its temperature before and after 

 contraction ; and (c) the specific heat of muscle, are known. 



The specific heat of muscle is slightly greater than that 

 of water, but the difference is so slight that it may be 

 disregarded. If, then, a muscle of ten grams had a tempera- 

 ture of 15 C. before it was made to contract, and a temperature 

 of 15'05 C. after a period of contraction, then 0'5 gram- 

 degrees of heat have been produced ; i.e. heat sufficient to raise 

 the temperature of 0'5 gramme of water through 1 C. The 

 heat units employed are the small and large calorie the 

 small calorie the heat required to raise one gram of water 

 through one degree Centigrade, and the large Calorie written 

 with a large C the heat required to raise a kilogram of water 

 through one degree Centigrade. 



The amount of heat produced by muscle in different 

 conditions varies so greatly that it is unnecessary to consider 

 it further. 



Relationship of Heat Production to Work Production. 

 Siuce it is possible to measure both the mechanical work 



