HUMAN LONGEVITY. 107 



globe ; that others are probably in progress towards extinc- 

 tion ; and that no new creation is known within this period, 

 of animals of equivalent size to replace those thus vanishing 

 from the earth. It is also true that many of the domesticated 

 species, serving to the uses of man, have been largely in- 

 creased in numbers in effect of the increase of human popu- 

 lation on the globe. But these things, which are true, are 

 not new; and the doctrine derived from them that a 

 balance is struck between the two opposed conditions, and 

 that the total quantity of life, or of living beings, remains 

 always nearly the same is one wholly unsupported by the 

 premises. Its wording, in fact, betrays the author's hesitation 

 as to its truth. The ( a pen pres ' is a great discounter of 

 realities in science, as in most other things. 



It will be obvious indeed to all who care to reason on the 

 subject, that we have no knowledge, or means of obtaining it 

 otherwise than by vague approximation, as to the total quan- 

 tity of life on the globe, or the relative quantity at different 

 periods. Such phraseology then, except as denoting mere 

 hypothetical questions, cannot rightly be admitted into scien- 

 tific language ; seeing especially how little we are able to 

 estimate numbers or individualities of life in any of the 

 great classes of the animal kingdom ; how impossible it is 

 to conjecture them in the multitude of those lower forms 

 which we reach only through the eye of the microscope. 

 Nor in fact can any such conclusions as those put forward by 

 M. Flourens be accepted, as long as doubts exist as to the 

 proper definition of species, and the possibility of their 

 change or transmutation in long periods of time. We may 

 not acquiesce in these doubts, but the question is one fully 

 open to future enquiry. 



Dismissing however this subject, which it is not necessary 

 to pursue further, we come to the main topic of M. Flourens's 



