7ii.] ON THE PHYSICAL BASIS OF LIFE. 135 



salts, though it would be surrounded by all the consti- 

 tuents of protoplasm. Nor, indeed, need the process of 

 simplification of vegetable food be carried so far as this, 

 in order to arrive at the limit of the plant's thaumaturgy. 

 Let water, carbonic acid, and all the other needful con- 

 stituents be supplied with ammonia, and an ordinary 

 plant will still be unable to manufacture protoplasm. 



Thus the matter of life, so far as we know it (and we 

 have no right to speculate on any other), breaks up, in 

 consequence of that continual death which is the con- 

 dition of its manifesting vitality, into carbonic acid, 

 water, and ammonia, which certainly possess no proper- 

 ties but those of ordinary matter. And out of these 

 same forms of ordinary matter, and from none which 

 are simpler, the vegetable world builds up all the proto- 

 plasm which keeps the animal world a-going. Plants are 

 the accumulators of the power which animals distribute 

 and disperse. 



But it will be observed, that the existence of the 

 matter of life depends on the pre-existence of certain 

 compounds ; namely, carbonic acid, water, and ammonia. 

 Withdraw any one of these three from the world, and. all 

 vital phenomena come to an end. They are related 

 to the protoplasm of the plant, as the protoplasm of the 

 plant is to that of the animal. Carbon, hydrogen, oxygen, 

 and nitrogen are all lifeless bodies. Of these, carbon 

 and oxygen unite, in certain proportions and under 

 certain conditions, to give rise to carbonic acid ; 

 hydrogen and oxygen produce water • nitrogen and 

 hydrogen give rise to ammonia. These new compounds, 

 like the elementary bodies of which they are composed, 

 are lifeless. But when they are brought together, 

 under certain conditions they give rise to the still 

 more complex body, protoplasm, and this protoplasm 

 exhibits the phenomena of life. 



