METABOLISM 



after the ingestion of 170 grams of white bread as described in Experiment 3(b), 

 page 567. Plot a curve for these values similar to the one shown in Fig. 169, page 

 566. On a later day repeat the experiment and ingest 1 70 grams of white bread and 

 85 grams of butter. Plot the curve for these blood sugar concentrations along with 

 blood sugar values obtained after the ingestion of white bread as described above. 

 Has the fat exerted any influence upon the absorption of the carbohydrate? Re- 

 peat the above experiment on a case of diabetes mellitus if such is available and 

 note that fat exerts the same influence upon carbohydrate absorption as it exerts in 

 the normal human body. 



7. Time Relations of Protein Metabolism.- It is a well-known 

 physiological fact that an interval elapses between the ingestion of protein 

 food and the appearance in the urine of certain products representing the 

 complete catabolism of this food. For example, if one ingests an excess 

 of protein material an interval elapses before the urine gives evidence 

 of the complete excretion of certain products representative of the 

 catabolism of the protein. Urea is the chief of these. The term " nitro- 

 gen lag' 7 has been used to designate the period elapsing between the 

 ingestion of protein and the excretion in the urine of a quantity of 

 nitrogen equivalent to that contained in the protein. 



Experiment. Ingest a simple uniform diet whose exact composition has been 

 determined by analysis or whose approximate composition has been estimated. 

 (See table below.) Continue this diet from one to four days. Collect the 

 urine in two-hour periods from 7 A. M. to n P. M. and in an eight-hour period be- 

 tween n P. M. and 7 A. M. Analyze each specimen for total nitrogen or urea. 

 At the end of this preliminary period add to the uniform diet, at one meal, a 

 weighed quantity (150-250 grams) of lean meat specially prepared and analyzed. 

 Collect the urine in periods as before and determine total nitrogen or urea. 

 Calculate the total nitrogen or urea excretion; tabulate the data and plot curves 

 showing the course of the nitrogen excretion on the various days of the experi- 

 ment. How long was the "nitrogen lag?" 



COMPOSITION OF COMMON FOODS' 



1 Sherman's "Food Products," Macmillan, 1914. 



