4 WHAT IS LIFE 



outlined are by no means universally accepted and 

 that at any moment further facts may come into 

 notice which may utterly upset both this and the 

 earlier hypothesis. But the example will suffice to 

 show how uncertain even the oldest and most 

 respectable scientific theories may really be, and 

 will also serve as an excellent parallel to the 

 changes of opinion which have taken place in con- 

 nection with the question with which this present 

 book is concerned, that is the nature of life and of 

 living things. 



Those biologists if we may so speak of them 

 who flourished at the same time that the alchemists 

 were endeavouring to discover the philosopher's 

 stone, had no doubt at all as to the existence of 

 some further factor in living things than those 

 which were to be met with in inorganic objects. 

 Scholastics Fr. Maher * tells us that " the principle of life in 

 n the lower animals was held by the schoolmen to be 

 an example of a simple principle which is never- 

 theless not spiritual, since it is altogether depen- 

 dent upon the organism, or, as they said, completely 

 immersed in the body. St. Thomas accordingly 

 speaks of the corporeal souls of brutes." In fact 

 the scholastic philosophy assigned what it called 

 " souls," sensitive and vegetative souls, to vege- 

 tables as well as to the lower animals, and by that 

 1 Psychology, 5th ed., p. 469. 



