PROXIMATE CONCEPTION OP LIFE. 81 



Meanwhile, it is possible to frame a more adequate formula 

 than any of the foregoing. As we shall presently find, these 

 all omit an essential peculiarity of vital changes in general 

 a peculiarity which, perhaps more than any other, distin- 

 guishes them from non-vital changes. Before specifying this 

 peculiarity, however, it will be well to trace our way, step 

 by step, to as complete an idea of Life as may be reached 

 from our present stand-point; by doing which we shall both 

 see the necessity for each limitation as it is made, and ulti- 

 mately be led to feel the need for a further limitation. 



And here, as the best mode of determining what are the 

 traits which distinguish vitality from non-vitality, we shall 

 do well to compare the two most unlike kinds of vitality, and 

 see in what they agree. Manifestly, that which is essential 

 to Life must be that which is common to Life of all orders. 

 And manifestly, that which is common to all forms of Life, 

 will most readily be seen on contrasting those forms of Life 

 which have the least in common, or are the most unlike.* 



i 



25. Choosing assimilation, then, for our example of 

 bodily life, and reasoning for our example of that life known 

 as intelligence; it is first to be observed, that they are both 

 processes of change. Without change, food cannot be taken 

 into the blood nor transformed into tissue; without change, 

 there can be no getting from premisses to conclusion. And 

 it is this conspicuous display of changes which forms the 

 substratum of our idea of Life in general. Doubtless we see 

 innumerable changes to which no notion of vitality attaches. 

 Inorganic bodies are ever undergoing changes of temperature, 

 changes of colour, changes of aggregation; and decaying 

 organic bodies also. But it will be admitted that the great 



* This paragraph replaces a sentence that, in The Principles of Psy- 

 chology, referred to a preceding chapter on " Method ; " in which the mode of 

 procedure here indicated was set forth as a mode to be systematically 

 pursued in the choice of hypotheses. This chapter on Method is now 

 included, along with other matter, in a volume entitled Various Frag- 

 ment*. 



