CONDITIONS ESSENTIAL TO NUTRITION. 59 



but the manner in which they were instituted is op- 

 posed 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 conditions ; and 

 should but one of these be wanting, although 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 substances of the most differ- 

 ent 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 nutriment 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 

 exclusion of, all other substances. Can it be con- 

 cluded 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 constitu- 

 ent elements of its own substance, and are capable 

 of undergoing transformation. All the organs to- 

 gether cannot generate a single element, carbon, ni- 

 trogen, or a metallic oxide. 



When the quantity of the food is too great, or is 

 not capable of undergoing the necessary transform- 

 ation, or exerts any peculiar chemical action, the or- 

 gan itself is subjected to. a change : all poisons act 

 in this manner. The most nutritious substances may 

 cause death. In experiments such as those describ- 

 ed above, every condition of nutrition should be con- 

 sidered. Besides those matters which form their 

 principal constituent parts, both animals and plants 



