ADDRESS. 13 



plants have the power, by a galvanic agency, of eliminating 

 from the soil many important principles, not otherwise separa- 

 ble; nor is it more doubtful, that the various products of 

 plants are the result of a similar galvanic agency exerted by 

 their organs. The necessity of heat for effecting these various 

 changes has always been known ; but it is not till recently that 

 the necessity of light, and its mode of action, were understood. 

 The sap, it appears, undergoes but little change till it reaches 

 the leaves. There it experiences digestion, by the action of 

 solar light upon the green matter, called chloropylle. The 

 green matter itself is first produced, and then it forms an ap- 

 paratus by which the compounds in the sap are decomposed, 

 the oxygen gas is liberated, and mineral or inorganic matter 

 becomes organized, that is, converted into the various parts of 

 the plant. The chemist cannot, indeed, look into all the cru- 

 cibles, and flasks which nature employs in this curious labora- 

 tory, nor examine all the re~agents, be cause they are too 

 minute ; but he can see enough to show that the whole is a 

 chemical process, modified somewhat by the vital principle. 



He can see enough to make him strongly desire to see more • 

 enough to make him feel how infinitely superior is nature's 

 chemistry to his own. 



The analysis of the various parts and products of plants has 

 disclosed some most curious facts as to their great similarity, 

 and their relation to the principles found in animals. It has 

 been ascertained that animals need two sorts of food ; one 

 kind containing nitrogen, and another sort destitute of it. 

 Those principles containing nitrogen are necessary for their 

 nourishment, such as albumen, Jibrine, hcBmatin and caseine, 

 which are the same essentially in composition. Those princi- 

 ples destitute of nitrogen are necessary to sustain the process 

 of breathing, and thus to furnish fuel for keeping up the ani- 

 mal heat. These are fat, starch, sugar, gum, &c, Now these 

 principles, both for giving nutrition and keeping up the ani- 

 mal heat often exist ready formed in vegetables, and, when 

 vegetables are taken for food, the animal merely appropriates 

 the principles. Thus fat exists in the oily and waxy parts of 



