CONCLUSIONS 105 



pieces under a very slight stimulus. It has often thus 

 been represented. But this, after all, is a static view. 

 We have discovered this very fundamental fact, that 

 the resting metabolism goes faster when the tissue is 

 more abounding in life and is more irritable. It is the 

 burning substance which is irritable, or, perhaps, the 

 carbon dioxide thus formed conditions in some way 

 the vital or irritable reaction. It requires the expendi- 

 ture of energy to keep living matter in an irritable state. 

 The reaction is dynamic and not static. Living matter 

 has been conceived by many physiologists (of whom I 

 may mention only one of the leading exponents, Verworn, 

 for the various modifications of this view of individual 

 authors are not fundamental modifications) as being 

 composed of very complex unstable molecules, or aggre- 

 gates of molecules which are very unstable. These 

 are called biogens. Now this view is essentially static. 

 There is no reason why a biogen should not be isolated 

 if our methods were but fine enough. There is no reason 

 why a collection of biogens should not exist without any 

 metabolism; why, in other words, suspended anima- 

 tion should not be possible. But the facts which we 

 have discovered of the parallelism of the production 

 of carbon dioxide and irritability lend support, it would 

 seem, to the dynamic, rather than to the static, view. 



We can picture the process, perhaps, in the following 

 crude and, of course, indefinite manner: The life- 

 process may be considered as a bicycle in motion. The 

 living process is an unstable condition. It is like a 

 chemical system, the system as a whole having a certain 

 stability, but being at the same time the seat of intense 

 chemical change. It is in an unstable equilibrium. The 



