28 THE ORIGIN OF LIFE 



This irritability is often considered a test of life, 

 but not accurately so. All these properties imply a 

 relationship between the internal processes in the in- 

 dividual and its external environment. In other 

 words, as Herbert Spencer has put it, Life is the 

 continuous adjustment between the internal relations 

 of an individual or organism and its external relations 

 with its environment : an idea which runs througlf 

 the whole of his Biology and Sociology. 



Although all the six conditions we have described 

 are included in this definition, or, to put it more 

 accurately, the definition includes all those processes 

 we have mentioned in the six conditions of life, it 

 may include many others without in any way afiect- 

 ing it. The definition is at once adequate and 

 precise, and does not in the least imply more than 

 is essential to vitality in elementary forms. We may 

 also regard life from another but equivalent aspect, 

 though more suitable to our purpose because more 

 general. As Huxley has put it, living matter or 

 protoplasm, and the products of its metamorphosis, 

 may be regarded under four aspects : — 



(1) It has a certain external and internal form, 

 the latter being more usually called structure. 



(2) It occupies a certain position in space and time. 



(3) It is the subject of the operation of forces, 

 in virtue of which it undergoes internal changes, 

 modifies external objects, and is modified by them ; 

 and 



(4) Its form, place and powers are the effects of 

 certain causes. 



