RELATIONS BETWEEN MIND AND MATTER. 87 



gence. Once there seemed to be sufficient reason for dividing liv- 

 ing things into plants and animals. That was when knowledge 

 was fragmentary ; but now there is no line between them, 

 and no naturalist can so define one as to exclude the other. 

 The possession of what is called irritability, by which is meant 

 ability to respond by movement of some kind to an external 

 stimulus, is no longer a peculiar characteristic of what have 

 been called animals, for there are many plants that possess it 

 in a marked degree ; and there are free swimming plants, such 

 as bacteria. Experimental research with the microscope has 

 shown that this quality exists in all plants in some degree, and 

 that in all cases the reaction, of whatever kind it may be, shows 

 evidence of what, in higher forms of living things, is always 

 attributed to intelligence; that is, the reaction is adaptive. 

 This does not mean what in higher living things we call choice, 

 but it does mean that the energy resident in the organism 

 works spasmodically, automatically, and mechanically in a very 

 wonderful manner, and gives rise to phenomena which have 

 been thought could only appear where there was some kind of 

 animal existence as distinct from a vegetable. The discovery 

 of sensitivity as a quality belonging to all plants is new, and 

 makes it still more important that one should inquire further 

 as to whether other distinctions are as real as they have been 

 thought to be. Once a vital force was believed to be resident 

 in living things, and this force was supposed to control diges- 

 tion, nutrition, growth, and feeling,' but all biologists have 

 discarded the idea. I do not know of a single naturalist of 

 any distinction in the world who does not think and say that 

 all the phenomena exhibited by plants and animals are due to 

 physical and chemical causes alone. In a late lecture Professor 

 Stokvis, of Amsterdam University, said : " Certain it is that 

 life is a chemical function," and he thinks it is proved beyond 

 a peradventure. To present the evidence for it would be to 

 make a book ; and seeing that it is so generally accepted in 

 scientific quarters, where it would first meet opposition if it 

 could be opposed, one may accept it, at any rate, provisionally. 

 But what is meant by life ? Well, in brief, it means the 

 sum of the activities possessed by living things, including 



