520 MAINTENANCE EXCHANGE AND GROWTH 



Question of Part Taken Toy Elemental Nitrogen and 

 Hydrogen in Metabolism. The advances in technique of 

 respiration investigation have done away with the old sub- 

 ject of debate as to the part taken by nitrogen as an element 

 in the processes of metabolism. The final proof that no nitro- 

 gen in free condition is ever eliminated from the body and 

 that the statements to the contrary by other authors are due 

 to errors of observation has been attained through the care- 

 ful investigations of Carl Oppenheimer 13 and of Krogh. 14 

 Oppenheimer was able to show, too, that elemental hydro- 

 gen has just as little to do with metabolism as does nitrogen, 

 and that even when in high tension in the blood hydrogen 

 does not undergo combustion in metabolism. 15 Ammonia, 

 which is occasionally met in exhaled air, to all appearances is 

 due merely 'to processes of decomposition going on in the 

 mouth and bronchial tubes. 16 



MAINTENANCE EXCHANGE AND GROWTH 



The possibility of continuing respiration experiments on 

 human beings for a very long time and under nearly normal 

 conditions makes it also possible to determine the exchange 

 taking place in maintenance. A. Lowy states : ' ' By the term 

 maintenance exchange may be understood that basic volume 

 of metabolism which (excluding those tissue activities pro- 

 viding for transient requirements or producing extra ef- 

 forts) is essential for the maintenance of the continuous vital 

 functions. The maintenance metabolism of every adult in- 

 dividual presents a constant volume which remains uniform 

 for years and decades of years, as long as the body char- 

 acteristics of the individual do not become changed to an 



12 C. Oppenheimer (Zuntz's Lab., Berlin), Biochem. Zeitsehr., 1, 177, 1906; 

 4, 328, 1907. 



"A. Krogh (Copenhagen), Sitzungsber. d. Wiener Akad., 115'", 1906; cf. 

 therein Literature. 



15 C. Oppenheimer (Zuntz's Lab., Berlin), Biochem. Zeitschr., 16, 45, 1908. 



16 Literature upon the Composition of Exhaled Air : A. Jaquet, Ergebn. d. 

 Physiol., 2, 463-468, 1902; A. Lowy, ibid., 4', 144-154, 1908. 



