48 WHAT IS LIFE 



with a certain gas, should set up a quasi- efferves- 

 cence in the mouse which would cause move- 

 ment. Or again it may be vital, that is that the 



mouse moves because it chooses to move and is 

 i 



actuated to that choice by the sight of danger, by 

 the smell of food, by the call of another mouse or 

 what not. 



We may, of course, exclude the first form of 

 movement, for in it the mouse is as passive as the 

 stone and is moved in no other way than a stone 

 when it is cast from the hand. 



As regards the other or chemical explanation, 

 one must commence by making it clear that the 

 comparison of the gas and the effervescence used 

 above was employed as a very rough simile, pur- 

 posely rough in order to make clear the kind of 

 series of incidents which might be postulated, but 

 hopelessly crude when applied to a body the main 

 phenomena in which are based on the behaviour 

 of the colloid substances of which it is built up. 

 Of these substances and their behaviour we at 

 present know very little, and most people would 

 say that to dogmatise and generalise on that little 

 is, in the face of the many reconstructions which 

 new facts are almost sure to entail, to say the least 

 of it a very unwise proceeding. However that is 

 just what has been done, and the writer in question, 

 after dealing with the subject of tactisms, of which 



