CONDITIONS ESSENTIAL TO NUTRITION. 39 



tive proofs, that carbonic acid will not nourish 

 plants ; but the manner in which they were insti- 

 tuted is opposed to all rules of philosophical inquiry, 

 and to all the laws of chemistry. 



Many conditions are necessary for the life of 

 plants ; those of each genus require special condi- 

 tions, and should but one of these be wanting, 

 although all the rest be supplied, the plants will 

 not be brought to maturity. The organs of a 

 plant, as well as those of an animal, contain sub- 

 stances of the most different kinds ; some are formed 

 solely of carbon and the elements of water, others 

 contain nitrogen, and in all plants we find metallic 

 oxides in the state of salts. The food which can 

 serve for the production of all the organs of a plant, 

 must necessarily contain all its elements. These 

 most essential of all the chemical qualities of nutri- 

 ment may be united in one substance, or they may 

 exist separately in several ; in which case, the one 

 contains what is wanting in the other. Dogs die 

 although fed with jelly, a substance which contains 

 nitrogen ; they cannot live upon white bread, sugar, 

 or starch, if these are given as food, to the exclu- 

 sion of all other substances. Can it be concluded 

 from this, that these substances contain no elements 

 suited for assimilation ? Certainly not. 



Vitality is the power which each organ possesses 

 of constantly reproducing itself ; for this it requires 

 a supply of substances which contain the consti- 

 tuent elements of its own substance, and are capable 



