THE president's ADDRESS. 365 



a much more exact knowledge of the physical and chemical nature 

 of the living substance and its activities ; and we are as yet very 

 ignorant with regard to the simplest forms of life, their occurrence, 

 species, activities and structure. I will only attempt, therefore, 

 to consider some of the consequences of each theory. 



On the Lankesterian theory, we can understand why life does 

 not now originate on the earth under ordinary circumstances, 

 natural or artificial ; and it follows from the theory that all life 

 known to us has a common origin from a form or forms called 

 into existence at a particular epoch under special circumstances. 

 But if life has been generated from lifeless matter at any time, it 

 should be possible, in the abstract at least, to imitate and repeat 

 the circumstances under which it arose, were they known to us, 

 and thus generate life again. 



On the Arrhenian theory, life may have started its develop- 

 ment and evolution many times on the earth, and fresh germs 

 may be falling on the earth now. The statements of some of 

 those who have positively affirmed the occurrence of spontaneous 

 generation might be explained, conceivably, by supposing an 

 Arrhenian germ to have fallen into their cultures, though for my 

 part I am much more inclined to attribute their results to untidy 

 and inexact technique. 



In short, if life was generated on the earth, it should be possible 

 to generate it again ; and if new germs of life are coming to the 

 earth continually, it should be possible at some time to intercept 

 them and examine them ; but whether either of these possi- 

 bilities is capable of ever being realised is more than any man 

 can say. 



The two theories bring us down, as I have pointed out, to the 

 bed-rock of philosophical speculation, to the two opposed stand- 

 points of vitalism and mechanism, the difference between which 

 may be illustrated by a fictitious example. Suppose it were 

 possible to imitate artificially the structure and fabric of a living 

 organism, say of some plant, to such a degree of exactitude that 

 the mimic resembled the model not only in the minutest details 

 of structural arrangement of all its parts, but also in the chemical 

 composition, molecule for molecule, in each corresponding part. 

 Would then the mimic have the same properties as the model 

 that is to say, would our artificial plant be living? Without 

 hesitation the mechanist answers Yes, the vitalist No. To the 



