66 



FOODS A^D NUTRITION 



uble forms enter into the structure of important parts of 

 the body. For example, in the fluids of the body we find 

 common salt (chloride of sodium) as well as chlorides of 

 potassium, ammonium, etc., while important parts of our 

 bones are the insoluble carbonates and phosphates of cal- 

 cium. Mineral salts all agree in being unburnable, and it 

 is by burning foods and examining the character and 

 amount of the unburned residue that we are enabled to 

 determine the kinds and amounts of salts present in a 

 given food. (See Ex. XVII.) 



Water. — This liquid forms a large proportion of all 

 fresh vegetable and plant foods. It constitutes nearly 59% 

 of the weight of our bodies. This latter fact indicates the 

 great importance of water as a nutrient. The fact that 

 water becomes a vapor and passes off 

 in that form into the air when heated, 

 enables us by drying a substance in a 

 warm place to determine its water con- 

 tent. (See Ex. XVIII.) The loss of 

 weight represents the M'ater evaporated. 



Composition of Foods. 



The extent to which these nutrients 

 occur in various forms of foods (see also 

 Ex. XX.) is indicated in Chart I., on 

 page 57. 



Sources of nutrients. — An examina- 

 tion of our ordinary food supply reveals 

 the fact that for most of our nutrients 

 we are dependent ultimately upon the vegetable world. 

 Our food, in general, is animal, vegetable, or mineral in 



Fig. 21 — Apparatus ar- 

 ranged for nutrient 

 experiment witli a 

 seedling. 



