370 THE EVOLUTION THEOEY 



living protoplasm, a ' vitalistic principle,' a ' life-force,' on the activity 

 of which these specific phenomena of life, and particularly the con- 

 tinually repeated alternation of disruption and reconstruction of the 

 living substance, dissimilation and assimilation, growth and multi- 

 plication, depend. It is just as difiicult to prove the converse, that it 

 is impossible that chemico-physical forces alone should have called 

 forth life in a chemical substance of very special composition. 

 Although no one has ever succeeded, in spite of many attempts, in 

 thinking out a combination of chemical substances which — as this 

 wonderful living substance does — on the one hand undergoes com- 

 bustion with oxygen and, on the other hand, renews itself again with 

 ' nutritive ' material, yet we cannot infer from this the impossibility 

 of a purely chemico-physical basis of life, but must rather hold fast 

 to it until it is shown that it is not sufficient to explain the facts, 

 thus following the fundamental rule that natural science must not 

 assume unknown forces until the known ones are proved insufficient. 

 If we were to do otherwise we should have to renounce all hope of 

 ever penetrating deeper into the phenomena. And we have no need 

 to do this, for in a general way we can quite well believe that an 

 organic substance of exactly proportioned composition exists, in which 

 the fundamental phenomena of all life — combustion with simultaneous 

 renewal — must take place under certain conditions by virtue of its 

 composition. 



How, and under what external conditions, such a substance 

 first arose upon the earth, from and of what materials it Avas formed, 

 cannot be answered with any certainty in the meantime. Who knows 

 whether the fantastic ideas of Empedocles in an altered form would 

 not be justified here? I mean that, at the time of the first origin of 

 life, the conditions necessary for many kinds of complex chemical 

 combinations may have been present simultaneously on the earth, 

 and that, out of a manifold variety of such substances, only those 

 survived which possessed that marvellous composition which con- 

 ditioned their continual combustion, but also their ceaseless recon- 

 struction by multiplication. According to Empedocles, there arose 

 from chaos only parts of animals — heads without bodies, arms without 

 trunks, eyes without faces, and so on — and these whirled about in wild 

 confusion and flew together as chance directed them. But those 

 only survived which had united rightly with others so as to form 

 a whole, capable of life. Translated into the language of our time, 

 that would mean what I have just said — tha.t, of a large number 

 of organic combinations which arose, only a few, perhaps one, would 

 possess the marvellously adjusted composition which resulted in life, 



