HUMAN PHYSIOLOGY: INTRODUCTION 297 



tain carbon, oxygen and hydrogen. The green parts of plants 

 are, with the aid of sunlight, the manufacturers of starch. 

 The materials used are carbon dioxide (CO2) obtained from 

 the air by the leaves, and water obtained by the roots. 

 Thus vegetables and fruits supply the carbohydrate foods. 



Starch forms the chief carbohydrate food of the world. 



Carbohydrates unaided could not, however, form living 

 cells because they lack the element nitrogen, therefore, they 

 could not take the place of proteids. 



The carbohydrates, with the fats, have been called the 

 heat and energy producers because their compounds, in 

 becoming split up and oxidized, produce energy for the per- 

 formance of the body movements, and heat to maintain the 

 temperature of the body. 



The carbohydrates and fats have also been called "proteid 

 sparers" because by keeping up the supply of heat and 

 energy of the body they spare the proteids from that kind of 

 work so that their main work may be that of tissue formation 

 and growth. 



It would take relatively a very large amount of proteid to 

 furnish sufficient heat and energy. Therefore, if we should 

 furnish the body with enough proteid for this we should 

 over-furnish it with tissue-building material. It is thus 

 economy to furnish carbohydrate foods for heat and energy 

 and proteid for tissue-building. 



Test For Starch. — Break up and crush the substance to be 

 tested (a bit of potato or corn). Pour over it a few drops of iodine 

 solution. If there is a large amount of starch present it will turn black, 

 if but little starch is present it will turn blue. 



Test For Grape or Cane Sugar. — Heat the substance to be tested, 

 slightly, in a test tube with a little water. Add to this twice its bulk 

 of Fehling's solution* (may be obtained at the drugstore). Heat 



*To prepare Fehling's solution: 



Solution 1. — Add to 35 grains of copper sulphate (blue vitriol) 500 cubic 

 centimeters of water and put aside until dissolved. 



Solution 2. — Add to 160 grains of caustic soda and 173 grains of Rochelle 

 salts, 500 cubic centimeters of water. Mix equal parts of solutions 1 and 2, 



