THE WORD LIFE. 263 



be allowed that the difference is not merely a difference of 

 degree but of kind. 



We cannot prove that life results from, or is invariably 

 associated with certain definite chemical and physical- 

 actions, or that it is due to certain special external con- 

 ditions, for it is easy to adduce instances in which life is 

 manifested under varying, and even opposite and conflicting 

 circumstances. In short the conditions under which life 

 exists are so many and so variable that it is not reasonable 

 to attribute it solely to any conceivable combinations of 

 external circumstances unless indeed it is reasonable to 

 assume that the very same phenomena are a consequence of 

 the influence of very different conditions. Among many other 

 positive statements it has been asserted that life cannot 

 exist unless oxygen be present, but it has been proved that 

 certain forms of living creatures not only live and grow and 

 multiply in the absence of oxygen, but that this substance 

 exerts upon them a deleterious influence. In like manner 

 it will be found that other broad general statements as to 

 what is, and what is not necessary to life, break down as 

 soon as they are put to the test of actual observation. 



It has been supposed by some that a change in the 

 position of the matter will alone make all the difference as 

 regards the proper application of the term vital. It has 

 been held that a tissue should be called alive as long as 

 it remains attached to a living body, dead when detached, 

 irrespective of any changes that may have occurred in the 

 tissue itself. But it is obvious that, for example, a leaf, 

 or an elementary part, may be as devoid of life while it yet 

 remains attached to the living trunk as after its connection 

 has been completely severed. To assert that a dead leaf 



