THEORY OF MUSCULAR FORCE. 671 



being of the animal economy ? The truth is, that 

 this "slight difference" constitutes one of the most 

 important facts connected with the whole theory 

 of Physiology, Pathology, and Therapeutics. In 

 accordance with the views of the ancients, who 

 believed with Homer, that " strength is derived 

 from spirits and from blood," it is now com- 

 pletely established, that the contractile power of 

 the muscular system, whether voluntary or in- 

 voluntary, is directly in proportion to the quantity 

 of arterial blood with which they are supplied, 

 and the rapidity of its circulation through them. 

 But that caloric is the spirit on which its power 

 of maintaining their activity and strength de- 

 pends, is manifest from the facts already stated, 

 that if the temperature of the blood be not raised 

 above that of the solids, while passing through 

 the lungs where it is formed, it cannot unite with 

 their substance ; and that whenever the general 

 system is reduced below the natural standard by 

 the abstraction of its vital heat, or by a deficient 

 supply of it by respiration, all the energies of the 

 animal machine are proportionally diminished. 



On the other hand, whenever the temperature 

 of the living body is raised much above the 

 natural standard, so that the solids are brought 

 nearly to an equilibrium with that of the arterial 

 blood, the operations of secretion and nutrition 

 are nearly suspended, and all the energies of life 

 proportionally diminished. The reason of which 



