BASIC PRINCIPLES. 



25 



The chemical reaction may be expressed as follows : 

 C 12 H 24 12 + 12 2 = 12 C0 2 + 12 H 2 

 That is, for every 12 molecules of oxygen absorbed, there are produced 

 12 molecules of carbon dioxide. Accordingly, for every liter of oxygen 

 absorbed, there is produced one liter of carbon dioxide, so that the 

 volume ratio may be expressed : 



Volume C0 2 



= 1.00 



Volume 2 



We can say, therefore, that the respiratory quotient of lactose is 1.00. 

 This is also true of all carbohydrates, including starch, cane sugar, 

 levulose, and dextrose. 



Furthermore, it can be computed from the molecular composition 

 that 1 gram of human fat requires 2.844 grams of oxygen in its com- 

 bustion and that as a result of the combustion 2.790 grams or 1,420.4 c.c. 

 of carbon dioxide are produced. There is, therefore, an absorption of 

 1,990.8 c.c. of oxygen to form 1,420.4 c.c. 1 of carbon dioxide; hence the 

 respiratory quotient would be: 



Volume CQ 2 1420.4 _ 

 Volume 2 1990.8 



The calculation of the theoretical respiratory quotient of protein is 

 less simple, owing to the fact that protein is only incompletely oxidized, 

 a portion of the protein molecule being excreted unburned in the form 

 of urea, uric acid, and allied compounds in the urine. The calculation 

 of this quotient has been made in a number of ways by different writers 

 on the subject, each assuming a somewhat different molecular compo- 

 sition for protein and each ascribing in turn various values to the 



Table 13. — Assumed apportionment of elements after oxidation. 



unoxidized portion of the protein excreted in the feces as well as in the 

 urine. Furthermore, observers differ as to what degree the sulphur 

 of protein is oxidized, for unoxidized as well as completely oxidized 

 sulphur may be found in the urine. The following calculation is taken 

 directly from Loewy, 2 in which he assumes that 100 grams of fat-free, 

 dry substance of flesh contain 52.38 grams of carbon, 7.27 grams of 

 hydrogen, 22.68 grams of oxygen, 16.65 grams of nitrogen, and 1.02 

 grams of sulphur. The assumed apportionment after oxidation is 

 given in table 13. 



Erroneously stated as 1,240.4 c.c. by Benedict, Am. Journ. Physiol., 1909, 24, p. 348. 

 2 Loewy, Oppenheimer's Handbuch der Biochemie, Jena, 1911, 4, (1) p. 156. 



