220 THE PHENOMENA OF MOTION 



organ cannot produce in itself is conveyed to it 

 from other quarters ; and the vital force which is 

 wanting to it, in order to furnish resistance to ex- 

 ternal causes of disturbance, it receives in the form 

 of excess from another organ, an excess which that 

 organ cannot consume in itself. 



We observe further, that the voluntary and in- 

 voluntary motions, in other words, all mechanical 

 effects in the animal organism, are accompanied by, 

 nay, are dependant on, a peculiar change of form 

 and structure in the substance of certain living 

 parts, the increase or diminution of which change 

 stands in the very closest relation to the measure of 

 motion, or the amount of force consumed in the 

 motions performed. 



As an immediate effect of the manifestation of 

 mechanical force, we see, that a part of the mus- 

 cular substance loses its vital properties, its cha- 

 racter 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 (just as the acid lost its chemical 

 character by combining with zinc) ; and all experi- 

 ence proves, that this conversion of living muscular 

 fibre into compounds destitute of vitality is accele- 

 rated or retarded according to the amount of force 

 employed to produce motion. Nay, it may safely 

 be affirmed, that they are mutually proportional ; 



