2 OUTLINES OF EVOLUTIONARY BIOLOGY 



that living matter differs fundamentally from not-living matter 

 in chemical or physical characters. On the contrary we recog- 

 nize in it exactly the same chemical elements or rather some 

 of them as we find in other constituents of the earth, and 

 these elements appear to obey precisely the same chemical and 

 physical " laws " in both cases, but in the living body they are 

 associated and combined with one another in such a manner as 

 to give rise to substances much more complex than any found 

 outside the animal and vegetable kingdoms, and possessed of 

 peculiar properties which raise them to an altogether higher 

 plane of existence. The complex substances in question con- 

 stitute protoplasm, which is the one essential constituent of 

 every living thing, upon the peculiar properties of which the life 

 of the organism depends. 



We may begin our investigations into the nature of this life 

 by examining the well-worn but none the less valuable analogy 

 of the flame of a candle. Chemists and physicists have taught 

 us that flame consists of incandescent matter, raised to a high 

 temperature by the process of combustion, or chemical union 

 with the oxygen of the atmosphere, and that the flame can exist 

 only so long as the combustion goes on and a sufficiently high 

 temperature is thereby maintained to render the burning matter 

 luminous, or in other words to produce those vibrations of the 

 invisible and intangible ether which we recognize as light. The 

 flame, then, is the outward and visible sign of certain chemical 

 and physical processes, of the action and reaction between the 

 material which is being burnt and the atmosphere which 

 surrounds it. 



Similarly biologists have learnt to recognize life as the expres- 

 sion of the constant interaction which goes on between the living 

 organism and its environment, or, in the words of Herbert 

 Spencer, " the continuous adjustment of internal relations to 

 external relations." So far as we have yet been able to analyze 

 it, this interaction also consists of chemical and physical pro- 

 cesses, amongst which combustion plays a large part ; but the 

 whole business is vastly more complex than the processes 

 involved in the production of a flame, and so far many of its 

 details have defied analysis. 



We may vary our analogy by looking upon the body of a living 

 organism, whether plant or animal, as an extremely elaborate 

 engine or machine, whose existence depends upon a perfect 



