36 THE VITAL FUNCTIONS. 



elements are arranged. Although these several 

 principles possess very different sensible properties, 

 yet they are found to differ but very slightly in the 

 proportions of their ingredients ; and we may infer 

 that the real chemical alterations, which are required 

 in order to effect these conversions, are compara- 

 tively slight, and may readily take place in the 

 simple cellular tissue.* 



In the series of decompositions which are arti- 

 ficially effected in the laboratory of the chemist, 

 it has been found that gum and sugar are inter- 

 mediate products, or states of transition between 

 various others ; and they appear to be peculiarly 

 calculated, from their great solubility, for being 

 easily conveyed from one organ to another. Starch, 

 and lignin, on the other hand, are compounds of a 

 more permanent character, and especially adapted 

 for being retained in the organs. Starch which, 

 though solid, still possesses considerable solubility, 

 is peculiarly fitted for being applied to the purposes 

 of nourishment : it is accordingly hoarded in ma- 

 gazines, with a view to future employment, being 

 to vegetables, what the fat is to animals, a resource 

 for exigencies which may subsequently arise. 



> 



* According to the analyses of Dr. Prout, the following is the 

 composition of these substances : 1000 parts of 



Pure Gum Arabic consist of 586 of oxygen and hydrogen, united 

 in the proportions in which they exist in water, and 414 of 

 carbon. This, according to the doctrine of chemical equiva- 

 lents, corresponds to one molecule of water, and one molecule 

 of carbon. 



Dried Starch or Fecula of 560 water, and 440 carbon. 



Pure crystallized Sugar . . 572 428 



Lignin from Boxwood . . . 500 500 



Phil. Trans, for 1827, 584. 



