110 ON THE PHYSICAL BASIS OF LIFE 



raise the less complex substances carbonic acid, 

 water, and nitrogenous salts to the same stage of 

 living protoplasm, if not to the same level. But the 

 plant also has its limitations. Some of the fungi, for 

 example, appear to need higher compounds to start 

 with; and no known plant can live upon the uncom- 

 pounded elements of protoplasm. A plant supplied 

 with pure carbon, hydrogen, oxygen, and nitrogen, 

 phosphorus, sulphur, and the like, would as infallibly 

 die as the animal in his bath of smelling-salts, though 

 it would be surrounded by all the constituents of proto- 

 plasm. 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 constit- 

 uents be supplied except nitrogenous salts, and an 

 ordinary plant will still be unable to manufacture pro- 

 toplasm. 



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 nitrogenous compounds, which certainly 

 possess no properties 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 protoplasm 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 mat- 

 ter of life depends on the pre-existence of certain com- 

 pounds; namely, carbonic acid, water, and certain 

 nitrogenous bodies. Withdraw any one of these three 

 from the world, and all vital phenomena come to an 



