!xx INTRODUCTION 



upon his argument the title of a " proof of vitalism." Now 

 this argument fer exclusionem is sound, upon one condition 

 only ; and that is that all possible alternatives have really 

 been marshalled together at the outset of the argument. 

 This is a condition which, in the present state of physio- 

 logy, is entirely impossible to satisfy. It is interesting to 

 note that, of the various possibilities named by Lamarck, 

 not one figures in the list of possibilities named by Driesch. 

 A century has swept them all away, and brought out a 

 whole series of new possibilities, never dreamt of by Lamarck. 

 Few students of the history of science can doubt that another 

 century, or much less (for things move faster now) will 

 sweep away no less effectively Driesch's list of possibilities. 

 In order to name every conceivable mode of explanation of 

 any phenomenon, it is necessary to know infinitely more 

 about the conditions of that phenomenon than is at present 

 possible in any branch of physiology. We have to know 

 that we have exhausted every possible alternative ; we have 

 to know that there is nothing more to be known ; and that 

 is a condition of the most extreme stringency. This argu- 

 ment, or some attempt at it, has served as proof of every 

 kind of erroneous explanation of the universe, and all things 

 in it, great and small. The ancients vaguely used that 

 method when they affirmed the existence of animal spirits : 

 by the same method, Lamarck proved the existence of a 

 subtle, invisible nervous fluid racing up and down the 

 nervous system : by this method again, Driesch proves the 

 existence of a vital force. I challenge anyone to find the 

 slightest difference between Lamarck's method of proving 

 the existence of the nervous fluid, and Driesch's method of 

 proving the existence of the vital force. This logical method, 

 dignified by the name of per exclusionem, is indeed a method 

 of argument by which nearly all untrained minds, and a 

 great many trained minds, are wont to establish propositions 

 they desire, in place of the disagreeable confession of ignorance 

 or agnosticism. It is at the bottom of every vitalistic theory. 

 *' Here is a process difi&cult to explain : it cannot be caused 



