FOODOFPLANTS. 13 



may be considered as compounds of carbon with water, or more 

 properly with the elements of water, for it is not proved that water 

 exists as such in them. This affords a convenient way of stating 

 their composition. 



Carbon. Water. 



Starch, = 12 + 10 



Cane Sugar, 12 +11 



Gum, 12 + 11 



Sugar of Milk,... .12 -f 12 



Grape Sugar, 12 +14 



From this table it may be seen that these principles are convert- 

 ible into each other, simply by adding or subtracting the elements 

 of water. Some principles as, gum and cane sugar, are identical 

 in composition though different in properties. Such instances of 

 substances having different propertieswhile their composition is the 

 same, are also found in inorganic compounds. They are called 

 isomeric. Their differences are supposed to depend on a different 

 arrangement of their atoms. 



Among the non-nitrogenized principles, there are others in 

 which the oxygen and hydrogen are not united in the proportions 

 to form water. These are the oils and acids. 



The nitrogenized proximate principles are albumen, fibrin and 

 casein ; they are identical in composition with the principles of 

 the same name found in animals. These three^principles are nearly 

 identical in composition, differing only in the proportions of sul- 

 phur and phosphorus which exist in them in very minute quantities. 

 They may all be resolved into a principle called protein, composed 

 of carbon, oxygen, hydrogen, and nitrogen, combined with sulphur 

 and phosphorus. 



Thus, fibrin,.. = Protein, + P. + 2 S. 

 Albumen,.... = Pr. + P. + S. 



Casein, = Pr. + S. + 



These nitrogenized principles are of great importance in nutri- 

 tion, since all the organized tissues of animals are formed from 

 them. They are the only proper supporters of nutrition, and 

 vegetable food is nutritive in proportion to the amount of nitro- 

 genized principles it contains. The non-nitrogenized principles 

 . serve as supporters of respiration and not as supporters of nutrition. 



