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The Evolution of the Sciences 



truly specific characteristic and consequently 

 a definition of life. The same phenomenon is 

 found in a cauliflower stem or a plant of celery ; 

 death abolishes it in this case also. But if we 

 take a rod of tin or of any other carefully- 

 annealed metal, the same effect will be produced, 

 and it can be abolished under certain conditions 

 to be mentioned. 



One of the most characteristic features of 

 animal life is fatigue. If a frog's muscle is 

 subjected to a series of stimuli of equal force, 

 and repeated at equal intervals, the contractions 

 of the tissue, or the electric reactions indicated 

 by the galvanometer, will at first be equal, and 

 will then gradually become weaker, until a state 

 of permanent contracture is reached. The 

 tissue is tetanised. In living animals it is 

 possible to attribute fatigue to a sort of poisoning 

 of the tissues, caused by waste products and 

 toxins, when the supply of repairing elements 

 by the circulating blood is insufficient; and 

 yet a cut and bloodless muscle recovers its 

 excitability after a few moments of rest. It 

 will cause no great surprise if we say that 



vegetables also present unmistakable signs of 



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