METABOLISM 579 



certain of the constituents is uninfluenced by the amount of protein 

 ingested. Among these are creatinine and neutral sulphur. On the 

 other hand the output of inorganic sulphur and urea is more or less 

 directly proportional to the protein ingestion. The observation 

 of such facts as these led Folin to formulate his theory of protein 

 metabolism. 1 



Experiment. During a period of two or three days ingest an ordinary mixed 

 diet containing 100-125 grams of protein (16-20 grams of nitrogen) per day. 

 Collect the urine accurately in 24-hour periods (page 565) preserve it and analyze 

 the urine of the second and third days for total nitrogen, urea, creatinine, total 

 sulphur, inorganic sulphates, ethereal sulphates and neutral sulphur (by differ- 

 ence). For methods of analysis see Chapter XXVI. Follow this period by 

 one of three days in which a diet of starch and cream having a similar calorific 

 value is ingested. Analyze the urine for the second and third days as indicated 

 above. Calculate your results and tabulate as shown hi the table on page 578. 

 How did the change in the diet alter the metabolism of nitrogen and sulphur? 



In calculating the calorific value of a diet make use of the following values : 



i gram protein 4.1 large calories 



i gram fat 9.3 large calories 



i gram carbohydrate 4.1 large calories. 



18. Protein-Sparing Action of Carbohydrate and Fat. The non-nitrogenous 

 nutrients, carbohydrate and fat, have the power to diminish the extent of the catabo- 

 lism of protein in the normal human body. In other words they are said to "spare " 

 protein. This point is illustrated in data reported by von Noorden and Dieters, 

 which are tabulated below. 



PROTEIN-SPARING ACTION OF CARBOHYDRATE AND FAT 



Nitrogen ingested 



Nitrogen in urine 



12.6 grams. 10.4 grams. 





12.6 grams +200 grams sucrose. 9.0 grams. 13 per cent reduction in protein 



catabolism. 



It will be observed that the addition of 200 grams of sucrose to the diet was 

 accompanied by a decrease of 13 per cent in the amount of protein catabolized. 

 It has been established that carbohydrates are more efficient "protein sparers" 

 than are the fats. For example Voit found carbohydrate to produce a 9 per cent 

 decrease in protein catabolism whereas fats produced only a 7 per cent decrease. 



Experiment. Ingest a uniform diet of known or estimated nitrogen content 

 for a period of four days. Collect and preserve the urine accurately (see page 565) 

 in 24-hour samples and analyze the excretion of the third and fourth days for total 

 nitrogen. On the fifth day add 200 grams of sucrose to the diet. Analyze this urine 



1 The author's article on "General Considerations of Metabolism" in "Modern Medi- 

 cine" (Osier and McCrae) 2nd Edition, 1914, p. 594. See also Folin: American Journal 

 Physiol., 13, 118, 1905. 



