AUTHOR'S DEFINITION OF LIFE. 175 



degree of irritability in any part is necessarily in the 

 direct ratio of the quantity and quality of the irritable 

 matter which it contains." Further, that this matter 

 is " continually renewed and consumed by molecular 

 processes " in all vital acts. And again, that this 

 matter is in a state of combination so peculiar as to be 

 absolutely sui generis, and on which none of the 

 ordinary chemical agents and forces can act at all in 

 the way they do on non-living matter ; nor can they 

 cause ordinary matter to pass into this peculiar state. 

 That can only be done by pre-existing living matter, 

 and moreover, this matter cannot pass back to the 

 state of ordinary chemical combination, except by a 

 process of its own peculiar nature, i.e., its death as 

 well as its birth is a specially vital process (iii. 144). 

 Life is, therefore, not an entity, nor a force, but an 

 action and moreover, that action alone which is in- 

 volved in the consumption and regeneration, from 

 pabulum, of a material compound entirely sui generis 

 called irritable matter or protoplasm, under certain- 

 conditions and stimuli. Just as combustion is not the 

 materials for it, nor the product, nor the active force 

 evolved, but simply the act of chemical union; nor 

 does any supposed fire substance or element take part 

 in the process. Just as little does any life substance = 

 or principle, material or immaterial, take part in vital 

 processes. Our object is to reduce the idea of life to 

 its simplest form in order to distinguish between the 

 processes which are vital proper and those which are- 

 chemical and physical, all of which are engaged, more 

 or less, in making up the functions of even the simplest 

 order of individuality of living beings. The above 



