AN ESSAY ON LONGEVITY. 33 



had not, as the young, this under-stratum of ' vires 

 in posse ' to call upon in cases of exhaustion. ' We 

 must never forget to insist,' says M. Reveille Parise,^ 

 ' upon this fundamental principle, that the unknown 

 force of life, vis abdita qucedam, diminishes more and 

 more with the progress of age.' ' Ex viribus vivimus,' 

 said Galen.^ A young man is commonly said to 

 overtax his strength and to injure his constitution 

 by great expenditure of force when young. The 

 Common idea expressed in these various statements 

 of opinion is that a store of life-force or life- 

 material exists, which the young accumulate, which 

 increases up to a certain amount, but which ceases to 

 do so at some period, and thenceforward dwindles. 

 Professor Huxley has well expressed this in terms of 

 life-material, in a lecture delivered at Edinburgh, in 

 January, 1869. ' At any rate,' says Professor Huxley, 

 ' the matter of life is a veritable peau de chagrin, 

 and for every vital act it is somewhat the smaller. 

 All work implies waste, and the work of life results, 

 directly or indirectly, in the waste of protoplasm.' 

 Is there any direct evidence of the existence of such 

 a store of force or material as is evidently usually 

 supposed to exist in organisms.-' If we look at the 

 question from the point of view of force, it makes 

 little difference, for force implies matter in a particular 

 condition. It could not be maintained that one 



' Quoted by M. Flourens, loc. cit. 

 '' ' Method. Medend.' Lib. xi. 



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