CHEMICAL CHARACTERS OF CELL 87 



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, purposely 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 tact- 

 isms, of which mention has just been made, 

 states it as his opinion that " the irritability 

 peculiar to this cell species can be thus reduced 

 to a sum of perfectly well-defined tactisms " Tactisms 

 (the cell in question is the antherozoid of a 



