OF VITAL MOTION. 95 



if we had to do with a solid mineral, where under 

 these circumstances the action would be inconsiderable, 

 and where careful isolation is necessary to render it 

 sensible, but it is rather with a galvanic apparatus in 

 slow action, where there is large amount of sensible 

 force, notwithstanding the immense quantities which 

 steal off to the earth without any manifest trace. 



It is not difficult, therefore, to account for the effects 

 of mechanical irritation upon an electrical hypothesis, 

 without having recourse to any other law than that 

 which has been traced throughout these researches. 



The phenomena of muscular motion, in rela- 

 tion to the chemical aspect of the general force of 

 which heat, light, and electricity are correlative ex- 

 pressions, are mixed up with a large mass of dubious 

 theoretical notions; but at the same time we may 

 obtain some insight into this part of our subject from 

 the action of oxygen and carbonic acid upon the re- 

 spiratory organs, for while these gases are intimately 

 concerned in the normal workings of life, they at the 

 same time typify the two grand classes of chemical 

 agents which depress or exalt the vitality of the 

 system. 



In respiration the air passages alternately dilate 

 and become filled with air, and contract and expel 

 their contents; and these changes are excited by 

 certain vivifying properties of the atmosphere, which 



