THE PRODUCTION OF ENERGY IN MUSCLE 97 



raised a certain distance with every contraction, its descent being 

 guarded against by an automatic brake {B) which retains the wheel 

 in its newly acquired position during the subsequent resting period of 

 the muscle. At the end of this experiment the total work performed 

 by the muscle, may be computed by multiplying the weight by the 

 height to which it has been raised. 



The Muscle as a Thermogenic Organ. — We have seen that the 

 largest amount of the energy liberated by the body leaves it in the 

 form of heat. We are also justified in concluding that this heat is 

 derived very largely from the activity of the musculature, because the 

 latter constitutes about 40 per cent, of the total weight of the body and, 

 after the removal of the skeleton, more than 50 per cent. The bones, 

 as may readily be surmised, do not possess a vivid metabolism, while 

 that of the muscles is greater than that of any other tissue. Thus, 

 it is a matter of common experience that the temperature of the body 

 increases very markedly during exercise, frequently to 39° or 40° C, 



Fig. 53. — Arrangement of Thermoelectric Elements (A and B) and Gal- 

 vanometer C. 



but this rise is only temporary in its nature, because the heat is again 

 dissipated during the subsequent period of relative muscular rest. 

 The production of heat may also be registered locally in the contract- 

 ing muscles of the thigh or arm of a mammal, the bulb of a thermom- 

 eter being pushed in among the muscle fibers (Gierse, 1842). More 

 exact values, however, may be obtained with the help of thermoelec- 

 tric elements, but naturally, the thermoelectric method necessitates a 

 much greater experimental aptitude than the thermometric. 



A thermoelectric couple consists of two dissimilar metals, such as German 

 silver and iron or antimony and bismuth {A and B). These are soldered together 

 and the binding post upon each couple connected with a low resistance galvanom- 

 eter (C). In investigating the heat production of muscle, one of these couples is 

 inserted with its pointed tip in an indifferent muscle, while the other is placed in 

 the muscle to be experimented upon. As long as this muscle remains inactive, it 

 generates no heat, and hence, no electric differences are developed at the points of 

 soldering. The needle of the galvanometer remains stationary. If the muscle is 

 now made to contract, this system immediately ceases to be isoelectric, because the 

 heat produced therein generates an electric difference in the corresponding ther- 

 mopile which in turn leads to a definite deflection of the galvanometric needle. 

 7 



