SOLAR ORIGIN OF MUSCULAR FORCE. IO/ 



our bodies produces a direct liberation of heat instead of motion. 

 In the case of a person actually lifting a weight, the combustion 

 of his tissue is expressed in the motion of the weight ; but sup- 

 posing he only attempts to lift a weight which is too heavy for 

 him, there is then no production of motion, but instead of it a 

 corresponding increase of temperature in the muscle. In tetanus, 

 again, where the violent contraction of the muscles produces no 

 external motion, their temperature has been observed to rise as 

 much as six degrees centigrade or eleven degrees Fahrenheit 

 above the normal state. Conversely, in the case of a man work- 

 ing a treadmill, although the amount of heat evolved from his 

 person is absolutely larger, its proportion, relatively to the 

 amount of tissue burned, is smaller than in the case of a person at 

 rest, by a difference equivalent to the external work performed. 

 But in fever, where there is a rapid destruction of tissue without 

 any corresponding mechanical effect, we have a complementary 

 manifestation of external heat. 



(114.) Thus we return once again to the conclusion which I 

 brought more prominently under your notice in my last lecture. 

 We perceive that muscular exertion does not result from vital 

 force generated within the body, or, indeed, from force of any 

 kind generated within the body, but only from a liberation 

 within the body of pent-up solar force, which at some time or 

 other had been rendered latent in the separated carbo-hydrate of 

 our food on the one hand, and oxygen of our breath on the other. 

 As ingeniously observed by Dr. Tyndall, when speaking of the 

 sun, ' It is at his cost that animal heat is produced, and animal 

 motion accomplished. Not only is the sun chilled, that we may 

 have our fires, but he is likewise chilled that we may have our 

 powers of locomotion.' From the terms in which I lately referred 

 to the fiction of vital force, some physiologists who honoured me 

 by their presence seemed to infer that chemists and physicists 

 were insensible to those important distinctions existing between 

 living and dead matter, which they, on the other hand, profess to 

 explain by declaring the former to be possessed, and the latter 

 dispossessed, of vital force. I believe, however, that chemists 



