FOOD OF ANIMALS. 187 



Besides these organic matters, there are certain inorganic con- 

 "stituents, saline and earthy, deposited in vegetable and animal tis- 

 sues. They are called the inorganic constituents of vegetables and 

 ■animals. 



These proximate principles are, at the present time, produced 

 exclusively by vegetables. Ordinary chemical processes cannot 

 form them from their elements, and animals can, indeed, in some 

 cases, transform one principle into another, but cannot create any of 

 -them from inorganic matters. I say at the present time, because 

 geological observations demonstrate that there was a time when no 

 organic matter existed on the earth. At a subsequent period, ve- 

 getables, and then animals appeared, produced under conditions 

 and by the operation of causes which we cannot point out, and 

 which certainly do not exist at this day, for there are now no in- 

 stances of the formation of vegetables or of animals, except from 

 pre-existing beings of a like nature. 



In a former article I have undertaken to show how the water, 

 carbonic acid, and ammonia, existing in the soil and in the atmos- 

 phere, undergo transformations in the living plant, by which they 

 are converted into starch, gum, sugar, and other proximate princi- 

 ples. The materials out of which these principles are formed, now 

 exist both in the soil and atmosphere, but they may all be ulti- 

 mately traced to the latter source. The water of the soil originally 

 existed in the atmosphere in the form of va.por, and has been deposi- 

 ted by rain, dew, &c. The carbonic acid and ammonia of the soil 

 are generated by the decomposition of vegetable and animal sub- 

 stances, but these substances themselves were formed from the 

 carbonic acid and ammonia of the atmosphere. Consequently, all 

 the organic matters of plants may be traced to the atmosphere as 

 their ultimate source. The vegetable kingdom is formed from the 

 -atmosphere. 



The exception to this is found in the inorganic constituents of 

 I vegetables, which are derived from the soil by the disintegration 

 I and decomposition of the rocks, under the influence of various 

 physical and chemical agencies. 



An acquaintance with the composition and mode of nutrition of 

 vegetables, is a necessary introduction to the study of nutrition in 

 animals, because animals derive the matter of which they are 

 formed from vegetables. 



