18 THE MECHANISTIC THEORY OF LIFE 



with in the inorganic world, that we must 

 assume that the processes occurring in living 

 organisms are guided and determined by 

 some non-physical factor best known as the 

 ' vital force ' or * vital principle/ but in 

 recent times appearing under various other 

 names. This factor is assumed to act blindly 

 and unconsciously, and to be in action at all 

 parts of the body. The animists also assume 

 a non-physical factor ; and this they identify 

 with the soul, which is supposed, however, 

 to act sub-consciously. For the purposes 

 of the present argument the animists may, 

 perhaps, be classified along with the vitalists, 

 as the differences between them are for the 

 present purpose very small. 



Although outspoken vitalism has now 

 become somewhat exceptional among biolo 

 gists, or physiologists, and the prevailing 

 opinion is in favour of the mechanistic theory, 

 yet vitalism in a modified form seems to be 

 constantly cropping up in biological litera 

 ture. The reasons for this are, in part at 

 least, fairly evident. We have only to look 

 back to the writings of some of the leading 

 advocates of mechanistic ideas in biology to 



