THEORY OF VITAL ATTRACTION. 079 



actually the case, would appear from the rapidity 

 with which birds and mammalia convert the con- 

 stituents of dead matter into blood and their res- 

 pective tissues ; and from the fact, that a strong 

 man has been known to lift about ten times his 

 own weight from the ground, in opposition to the 

 force of gravity, while the cohesion or con- 

 tractility of a living muscle is about ten times 

 that of a dead one, ceteris paribus* But I have 

 shown that this power depends on the rapidity with 

 which the composition of the part is renewed by 

 fresh arterial blood, and is in proportion to the 

 amount of caloric that passes through it from the 

 lungs in a given time. For example, it is because 

 more caloric is received from the atmosphere, 



hydrogen, carbon, and nitrogen, so as to form the proximate con- 

 stituents of organized bodies. But Liebig informs us, in his late 

 excellent work on the Application of Organic Chemistry to Agri- 

 culture, that urea, allantoin, formic acid, and oxalic acid, which 

 are products of vital action, have been formed out of the body by 

 chemical action. I have shown, however, that the principal dif- 

 ference between the operations of ordinary chemistry and those of 

 life is, that the latter are more complex. They are also more 

 energetic and exalted in animals than in plants, because in the 

 former the organizing principle is continually renewed. The truth 

 is, that we cannot combine the elements of oxygen and hydrogen 

 together, so as to form water, any more than we can form blood, 

 or any other organized substance ; but only bring the materials 

 of which they are composed together, while nature performs the 

 rest. 



* The manner in which the contractile power of a muscle is 

 maintained by the perpetual influx of arterial blood, and dimi- 

 nished by cutting off the supply, may be partially illustrated by 

 the mechanical process of moistening a dry rope with water, which 



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