THE PRODUCTION OF HEAT IN MUSCLE 249 



is a definite ratio between work and heat. Only a certain small 

 proportion of the total energy can be utilised as work, the rest being 

 dissipated as heat. The exact proportion depends on the difference 

 of temperatures that is available in the machine, and in the best 

 engines at our disposal amounts to one-tenth. If the machine does 

 no work, the heat production is increased by the amount corresponding 

 to the work. The same is true to a certain extent in muscle. If a 

 muscle be allowed to contract and relax twenty times when loaded 

 by a weight, the total external work done will be nothing. If, how- 



FIG. 75. Diagram of Fick's Arbeitsammler or muscle crank, 

 a & is a counter-balanced lever, attached to the muscle M at ra. When the 

 muscle contracts, the catch c carries round the circumference of the wheel D 

 and so coils up the weight w round the axle of the wheel. When the muscle 

 relaxes, if c. 2 is in the situation of the^lotted line, the weight pulls the wheel 

 and lever back to its original position. If, however, c 2 be applied to D, the 

 backward movement of the wheel is prevented, and the muscle is extended 

 simply by the weight of the lever ab. Thus at each contraction the weight 

 is drawn a little higher, and external work is performed by the muscle. 



ever, the weight be attached to the axle of a wheel, which is provided 

 with a catch so that the weight can only be drawn up (Fig. 75), and 

 the muscle be allowed to pull at each contraction on the circum- 

 ference of the wheel, at each contraction work is done. It is found 

 that in the latter case the muscle is less heated than in the former, 

 and the difference is equivalent to the work done in raising the weight. 

 But as soon as we begin to alter the work by altering the weight, 

 we are at once met by the difficulty that increased tension augments 

 all the properties of the muscle, and with the same stimulus both 

 work and heat production are raised by increasing the load. In 

 fact the maximum amount of heat is produced when the muscle 



