LECTURE IV. 

 ORGANISM AND MECHANISM. 



1. 7s Organism More than Mechanism? 2. Chemical and 

 Physical Laws apply to Organisms. 3. Some Difficulties in 

 the Application of Physical and Chemical Formula to Organ- 

 isms. 4. Criticism of Mechanistic Descriptions of Everyday 

 Functions. 5. Criticism of Mechanistic Descriptions of 

 Animal Behaviour. 6. Difficulty of Applying Mechanistic 

 Formulce to Development. 7. Difficulty of Applying Mecha- 

 nistic Formula; to Organic Evolution. 8. Answers to Criti- 

 cisms. 



1. 7s Organism More than Mechanism? 



ACCORDING to KirchhofFs famous definition (1876), the 

 task of mechanics is " to describe completely and in the sim- 

 plest manner the motions which take place in nature ". 

 When we give a mechanical description of an occurrence 

 the eruption of Vesuvius, the bursting of the broom-pods, 

 or the curling of the non-living tendrils of a mermaid's purse 

 it is in terms of matter and motion, or in chemico-physical 

 terms which are believed to be reducible to those of matter 

 and motion. The mechanical account is as such entirely 

 satisfactory when it enables us to see a process as a con- 

 tinuous series of necessarily concatenated mechanical opera- 

 tions like those which occur in the slow movement of a 

 glacier, or like the successive explosions which mark the 

 extension of a rapidly spreading conflagration. We shall 

 use the slightly wider term mechanistic to include either a 

 matter-and-motion description, which is in the strict sense 

 mechanical, or a more dynamical description in which the 



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