ORGANIC PROCESSES OF PLANTS AND ANIMALS. 1011 



other alkalies, in the cold, without neutralising them. The 

 properties of murexan closely resemble those of uramile. Like 

 uramile, murexan boiled with water, red oxide of mercury and 

 a little ammonia, yields murexide. The composition of mu- 

 rexan and uramile, also, not differing much in 1 00 parts, Dr. 

 Gregory admits it to be possible that these two substances may 

 be essentially the same. 



CHAPTER XL 



SECTION I. 

 ORGANIC PROCESSES OF PLANTS AND ANIMALS. 



Without describing the structure of the organs of plants 

 and animals, I may state shortly the principal observations 

 which have been made respecting the food of plants and animals 

 and the chemical changes which it undergoes in the animal 

 economy, with the relation which subsists between plants and 

 animals. Besides secreting the lignin and cellulose which form 

 the basis of their own solid structure, plants elaborate in their 

 organs various substances destitute of structure, such as sligar, 

 starch, gum, resins, essences, fat oils, and the endless variety of 

 principles which the vegetable kingdom presents to the chemist 

 for examination. These principles are either contained in the 

 fluids of the plant, or are stored up in particular organs, or are 

 thrown off as excretions. 



The mode of formation of such principles in the plant and 

 the chemical agencies by which one principle is transformed 

 into another, have hitherto been very imperfectly traced, owing 

 to the difficulty of the investigation occasioned both by the 

 minuteness of the mechanism aud the obscure nature of the 

 decomposing forces which appear to preside in organic changes. 

 These forces, so far as we can judge, are chiefly of the catalytic 

 class, the azotised albuminous principles of plants having 

 specially the function of ferments, which react generally upon 

 other principles in the same manner, it may be supposed, 

 as we observe diastase to operate during the germination of 

 seeds in converting their starch into gum and sugar. Nature 

 appears to have produced and placed near each principle its pe- 



2 u u 2 



