604 PHYSIOLOGICAL CHEMISTRY 



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

 ment. How long was the "nitrogen lag?" 



A less accurate experiment than the above but one which yields 

 interesting data may be carried out as follows: 



Ingest a simple diet whose nitrogen content can be estimated with some 

 degree of accuracy (see table above). Collect the urine hi two-hour periods 

 from 7 A. M. to ii P. M. and hi an eight-hour period from n P. M. to 

 7 A. M. and analyze for total nitrogen or urea. The next day ingest the same diet 

 plus 150-250 grams of lean meat whose nitrogen content has been determined by 

 analysis or estimated. Collect the urine as upon the previous day and determine 

 its total nitrogen or urea content. Plot curves showing the course of the nitrogen 

 or urea excretion on each of the days. How soon after the ingestion of the large 

 quantity of meat did you note an increase in the nitrogen or urea excretion? 

 How many hours after the meal was the maximum quantity of nitrogen or urea 

 excreted? 



15. Influence of Purine-free and High Purine Diets. The uric acid 

 of the body has a two-fold origin, i.e., it may arise from the metabolism 

 of the purine (nuclein) material of body tissue (glandular organs in 

 particular) or it may arise from the ingestion of purine (nuclein) 

 material. That uric acid which arises from the first source is called 

 endogenous while that which arises from the second source is termed 

 exogenous. Secretory activity may also act to increase the endogenous 

 uric acid output. The urine will therefore contain uric acid even though 

 no precursor of the acid be ingested. We may also increase the uric acid 

 output markedly by ingesting a high purine diet. However, no matter 

 how much purine material is eaten, only a small part of this purine 

 material reappears in the urine as uric acid. In gout it is claimed 

 there is an accumulation of uric acid in the blood due to the fact that 

 the kidney has lost the ability to maintain the normal blood uric acid 

 level. In this disease the excretion of uric acid may be low before an 

 attack and increase considerably during an attack. The excretion of 

 exogenous uric acid in gout is also much slower than normal. 



Experiment. Ingest a purine-free diet containing about 16 grams of nitrogen 

 and consisting of egg, cheese, milk, starch, fruit, sugar and water for a period 

 of two days (for purine content of foods, see table, page 605). Determine or 

 estimate the nitrogen content (see table, page 602) and during the next two 

 days substitute sweetbreads, thymus or liver for all the nitrogen of the diet 

 maintaining the calorific value of the diet the same as before. Return to the 

 original purine-free diet for a third interval of two days. During the final period 

 of two days feed a diet of sweetbreads or liver containing 50 per cent more 

 nitrogen than that of the first sweetbread period. Collect the urine for each 

 of the eight days of the experiment and determine uric acid, and total nitrogen 

 or urea. Note the rise hi the uric acid output during the sweetbread periods. 

 The uric acid output on the purine-free diet is endogenous in origin. Tabulate 

 your results. The following data were secured by Taylor and Rose 1 in a similar 

 but much more carefully controlled test than that just outlined. 



1 Taylor and Rose: Jour. Biol. Chem., 14, 419, 1913. 



