584 PHYSIOLOGICAL CHEMISTRY 



From your experiments what do you conclude as to the relative efficiency of 

 acid and alkali in altering the reaction of the urine? 



21. Influence of a High Calorie Non -Nitrogenous Diet. If an 



individual fasts there is a combustion of a certain amount of protein 

 tissue each day of the -fast. The destruction of such tissue is rather 

 low on the first day due to the fact that the glycogen stores of the body 

 are being utilized to furnish the necessary energy. If an individual 

 instead of fasting, ingests a diet of high calorific value and very low in 

 nitrogen the output of nitrogen in the urine of the third or fourth day 

 will be less than on the third or fourth day in lasting. This is due to 

 the fact that the body derives sufficient energy from the high calorie 

 diet and there is less destruction of protein body tissues than occurs in 

 fasting. For a discussion of energy value of foods see "Determination 

 of Fuel Value of Foods," below, and the table on page 569. 



Experiment. Ingest a high calorie diet which is very low in nitrogen or 

 actually non-nitrogenous. A satisfactory diet may include sugar, butter, starch, 

 cream, agar-agar and water. (For energy values see below and table, page 

 568.) Ingest such a diet for three days. Collect the urine in 24-hour periods, 

 preserve and analyze it for total nitrogen, acidity and ammonia. Note the low 

 nitrogen excretion on the third day as compared with the nitrogen output of the 

 third day of fasting. If so desired, you may (at some later date) fast for three 

 days and repeat the above analyses for comparison. 



Determination of Fuel Value of Food. When organic substances are oxidized 

 or burned in the human body they liberate a certain amount of heat. This calorific 

 energy or heat value varies according to the type of organic matter undergoing 

 oxidation. Thus the proteins, fats and carbohydrates of the diet when they are 

 burned in the body yield different quantities of heat per unit of substance than do 

 organic acids, alcohol, etc. The energy values of pure protein fat and carbohydrate 

 are the following: 



Protein = 4 . i large calories per gram. 



Fat =9-3 large calories per gram. 



Carbohydrate = 4.1 large calories per gram. 



In arriving at the energy value of any given diet it is customary to burn weighed 

 samples of the various foods in an oxygen atmosphere in an apparatus called a 

 bomb calorimeter (see Fig. 172, page 586). By this means we may determine how 

 much heat is liberated when the ingested food is oxidized in the body. A correction 

 must be made for the incompletely oxidized substances of the urine and feces. A 

 large mass of data concerning the heat value of foods has been collected and tabu- 

 lated, and it is therefore possible to arrive at an approximate idea of the energy 

 value of a diet by calculation (see table, page 569). The bomb colorimeter shown 

 in Fig. 172, page 586, is one of the most satisfactory for actual determination of the 

 heat of combustion of organic substances. 



22. Metabolism in Fasting. The metabolism of a fasting man is 

 entirely different from the metabolism of a well-nourished person. 



