i8 INTRODUCTORY 



experience : responses to sensation are compli- 

 cated by the rivalry of conflicting feelings, and 

 the primary reaction may be checked. A caged 

 bird will not snatch food from the hand if it be 

 afraid of the person who offers it. But, even in 

 the lowest organisms, the sequence of action upon 

 sensation does not appear to be as inevitable as, 

 for instance, the response of iron filings to a 

 magnet : the humblest of them show appearances 

 of hesitation, of choice, which would be inexplic- 

 able in simple automata. And in one essential 

 particular the sensation and reaction of living 

 things differs from the effect of light upon a 

 photographic plate : it is attended by feeling 

 dim and vague no doubt in the lower ranks of the 

 animal and in the vegetable kingdom, but still 

 something which, higher up the scale, has been 

 elaborated into consciousness. 



Changefulness. Life, it would seem, can ally 

 itself with Matter only by driving Matter into a 

 state of continual change. The materials that 

 compose the vital organs of plants and animals are 

 never constant : elaborate compounds are built 

 up from the food only to be disintegrated and 

 expelled as waste. Individuals are, then, ever 

 changing their composition ; and by birth and 

 death the tribe is ever changing its individuals. 

 Nor by this process is merely one individual sub- 

 stituted for another : formed by contributions 

 from two parents, each new individual differs 

 from its predecessors. And as tribes change their 

 individuals, so does the kingdom change its 

 tribes. Of the species, animal and vegetable, 

 that are alive at present, but very few existed in 

 the days geologically not very remote when 

 the earth was dominated by enormous lizards, or 

 when it grew the dense forests of which coal-beds 



