ON MATTER AND FORCE. 71 



The Hallerian irritability was the best repre- 

 sentative of this stage of ideas. 



According to the latest ideas, the origin of 

 the motion must be some antecedent equivalent 

 motion. This is looked for in the chemical 

 changes in the nitrogenous or the non-nitro- 

 genous matter of the contractile texture or sur- 

 rounding blood. 



" No one," says Dr. Frankland, " possessing 

 any knowledge of physical science, would now 

 venture to hold that vital force is the source of 

 muscular power. An animal, however high its 

 organisation, can no more generate an amount 

 of force capable of moving a grain of sand than 

 a stone can fall upwards, or a locomotive drive 

 a train without fuel." 



Professors Liebig and Playfair, and others, 

 say that the chemical changes in the nitro- 

 genous matter of the muscles are the cause of 

 motion. 



Professors Frankland, Fick,* and others, say 

 that the mechanical work is much greater 

 than can be accounted for by the amount of 

 change in this matter, as measured by the urea 

 produced. They determine the amount of 



* Appendix II. 



