90 THE THEOKY OF EVOLUTION 



complex and highly changeable chemical combinations 

 and thus creates new springs of energy. This continuous 

 exchange of material, by which nothing else is attained 

 and striven for than the self-maintenance and multipli- 

 cation of its individuality, shows itself in the most 

 striking way in the external appearance and is therefore 

 utilized by many investigators in their definitions. 

 Thus, for instance, 0. Hertwig states : f Life (using a 

 general expression) displays itself therein that the cell, 

 by virtue of its own organization and under external 

 influences, suffers constant changes and develops powers 

 by which its organic substance, on the one hand, 

 under definite expressions of energy is destroyed, and, 

 on the other, is again renewed/ l 



All that has so far been stated shows that the 

 organisms possess a power of their own to strive to 

 attain certain purposes and that they only convert 

 and use inorganic material in their own interest. 



This conception is entertained also in one or another 

 form by the majority of modern biologists, 2 as, for 

 instance, by Cl. Bernard, 3 0. Hertwig, 4 K. E. v. Baer, 



1 Attg&meine, Biologie, p. 65. 



2 Christian philosophy has always taught this and has never accepted 

 that enigmatical ' vital force ' which should be a particular form of energy, 

 but has conceded to the organism a substantial principle as having a 

 purposeful striving power. 



3 Lemons sur les Phenomenes de la Vie-, I, Paris, 1879, p. 51. ' The vital 

 force (here = cause of unit direction) directs phenomena which it does not 

 produce ; the physical agents produce phenomena which they do not 

 direct.' II, p. 524 : ' The ultimate element of the phenomenon is physical, 

 the arrangement is vital.' 



4 Allgemeine Biologic, pp. 16, 18, 65. The same : Der Kampf urn 

 Kernfragen der Entwicklungs- und Vererbungslehre, Jena, 1900, pp. 75, 80. 



