22 THE SCIENTIFIC PRINCIPLES 



a secondary action, starch being first formed from 

 carbonic acid and water. 



Eef erring to the exercise of force, he argued that 

 the animal secretions must contain the products of 

 the metamorphosis of the tissues ; he concluded that 

 a starving man, with severe exertion, would secrete 

 more urea than the most highly fed individual in a 

 state of rest ; and he combated the idea that the 

 nitrogen of the food can pass into urea without 

 having previously become part of an organised tissue. 

 He said : — 



'As an immediate effect of the manifestation of 

 mechanical force, we see that a part of the muscular 

 substance loses its vital properties, its character of 

 life ; that this portion separates from the living part, 

 and loses its capacity of growth and its power of 

 resistance. We find that this change of properties 

 is accompanied by the entrance of a foreign body 

 (oxygen) into the composition of the muscular fibre 

 * * * ; and all experience proves, that this conversion 

 of living muscular fibre into compounds destitute of 

 vitality is accelerated or retarded according to the 

 amount of force employed to produce motion. Nay, 

 it may safely be affirmed, that they are mutually 

 proportional ; that a rapid transformation of muscular 

 fibre, or, as it may be called, a rapid change of matter, 

 determines a greater amount of mechanical force ; 

 and conversely, that a greater amount of mechanical 

 motion (of mechanical force expended in motion) de- 

 termines a more rapid change of matter/ 



Again : — 



'The change of matter, the manifestation of 

 mechanical force, and the absorption of oxygen, are, 

 in the animal body, so closely connected with each 

 other, that we may consider the amount of motion, 



