Eelations between Factors oe Metabolism. 217 



in the same table show a similar variation in the respiratory quotient even 12 

 hours after the last meal was taken. 1 



The respiratory quotient, therefore, as determined in experiments of this 

 nature and in experiments in which the nitrogen excretion in the urine was not 

 simultaneously determined, has only a general value as indicating approxi- 

 mately the nature of the material katabolized. Assuming an ordinary protein 

 disintegration of about 100 grams a day, it would be possible to compute in a 

 general way the relative amounts of carbohydrate and fat used, but as no direct 

 determination was made of the nitrogen, this computation would have but little 

 value. 



Earlier investigations. The respiratory quotient has been determined in 

 innumerable cases by means of other forms of respiration apparatus in which a 

 mouthpiece or nosepiece was used, and the hundreds of experiments of Speck 2 

 and of Zuntz 3 and his associates have all been made in such a manner as to give 

 values for the respiratory quotient which are reasonably correct. 



Eespiratory quotients have been determined with man by the Zuntz-Geppert 

 method under almost every conceivable condition of diet, muscular activity, and 

 rest. While the apparatus is not adapted for the accurate determination of 

 respiratory quotients during sleep, as it requires the strict attention of the 

 subject 4 to hold the mouthpiece in position and insure absence of leaks, yet, 

 since complete muscular relaxation is insisted upon by the best workers with 

 this apparatus, the results obtained on trained subjects are distinctly comparable 

 with the results obtained in our experiments during sleep, as has been pointed 

 out previously. The respiratory quotient, when obtained under these condi- 

 tions and combined with the determination of the nitrogen excretion in the 

 urine, has been the basis of the methods of indirect calorimetry developed by 

 Zuntz and his associates. Furthermore, while usually when exact results are 

 desired, urinary analyses are made simultaneously with the determination of 

 the respiratory exchange, it is quite common to determine the respiratory ex- 

 change and assume a relatively constant protein disintegration. The computa- 

 tion of the total katabolism and energy transformations by this method have 

 received extensive treatment by Zuntz 5 and his co-workers. Since, in the ex- 

 periments here reported, the energy transformations were directly measured, it is 

 unnecessary to utilize the respiratory quotients for this purpose. On the other 



1 At the moment of writing an investigation is in progress in the Nutrition Labora- 

 tory of the Carnegie Institution of Washington at Boston, Mass., on the influence of 

 the preceding diet upon the respiratory exchange 12 hours after the last meal. In 

 this investigation very marked differences in the respiratory quotients are found, 

 which depend upon whether the last meal of the preceding day consisted in large 

 part of carbohydrates or was relatively poor in carbohydrates. 



- Speck, Physiologie des menschlichen Athmens, Leipzig, 1892. 



3 See Loewy, Oppenheimer's Handbuch der Biochemie des Menschen und der Tiere. 

 Jena, 1908, 4, p. 179. 



4 See Roily and Hbrnig, Deutsch. Archiv f. klin. Med., 1909, 95, p. 74. 



3 See Magnus-Levy, Pathologie des Stoffwechsels, von Noorden's Handbuch der 

 Pathologie des Stoffwechsels, Berlin, 1906, 1, p. 206. 



