NITROGENOUS ORGANIC COMPOUNDS OF PLANTS 223 



process and yield proteoses and peptones. The insoluble 

 proteids are the most common form of proteids in foods. 

 Experiment 65. Obtaining insoluble proteids from oats. To 

 the residue left in the flask from Experiment 60, add 2 cc. NaOH 

 and 50 cc. water. After shaking and allowing half an hour (or 

 until the next day) for the extraction of the proteids, filter off the 

 solution and make the following tests: (i) Neutralize 5 cc. with 

 HC1, and if no precipitate appears, add a few drops of lead acetate; 



(2) neutralize 5 cc. with HC1 and evaporate to dryness on the 

 water-bath. 



Questions. ( i ) Why was NaOH used ? ( 2 ) What effect did the 

 HC1 and lead acetate have when added to the solution, and what 

 was formed? (3) How did this precipitate of insoluble proteids 

 from oats compare in amount with the globulin and albumin 

 precipitation in Experiments 59 and 60? (4) What is an insoluble 

 proteid ? 



305. Food Value of Proteids. The proteid com- 

 pounds of plant and animal bodies serve three purposes 

 as nutrients : ( i ) To produce new muscular tissue and 

 vital fluids in the body, and supply material for repairing 

 broken-down tissue ; (2) to produce heat and energy; 



(3) to assist in the production of fat. 



The main function of the proteids is to produce new 

 proteid tissue in the body, and to furnish a material for 

 the repair of old or worn-out proteid matter. The vital 

 fluids of the body, as blood, chyme, milk, and the diges- 

 tive fluids, all contain proteids, and the animal body is 

 incapable of producing any from either non-nitrogenous 

 or amide compounds. When the food fails to supply a 

 sufficient amount of protein, the body uses its reserve 

 supply as long as it lasts, and then starvation results. 

 When there is an excess of proteids in the food, it is 



