PART II. 



ANALYSES OF ATMOSPHERIC AIR MADE AT THE 

 NUTRITION LABORATORY. 



From the standpoint of pure physiological chemistry, the importance 

 of an exact knowledge of the composition of the air entering the lungs is 

 obvious when one attempts to consider the various means for studying 

 the respiratory exchange. Every living individual is continually taking 

 into the lungs air of a certain composition, which on leaving the lungs has 

 a different composition. By knowing the volume of air passing through 

 the lungs and the change in composition, important deductions with re- 

 gard to the metabolic processes can be made. Furthermore, in certain 

 lines of physiological experimenting, it is customary to confine a subject 

 inside an air-tight chamber through which a current of ventilating air is 

 passed, the changes in composition of the air inside the chamber being 

 accurately measured. Obviously, here again it is necessary to know the 

 exact oxygen content of the air entering the chamber. 



Although recognizing that the evidence thus far accumulated shows 

 slight differences in the percentage of oxygen in the air, experimenters for 

 the most part have been content to assume a constancy in this factor 

 for air supplied to a respiration chamber or entering the lungs through 

 nose-pieces or a mouth-piece in an apparatus requiring special appliances 

 for breathing. Singularly enough, however, while assuming a certain 

 degree of constancy, investigators have been at variance in regard to the 

 value to be assigned for the oxygen content of the air. In examining the 

 literature one finds, even in recent researches, variations in the assumed 

 composition all the way from 20.88 to 20.96 per cent. With the Zuntz 

 respiration apparatus and with the Chauveau and Tissot apparatus, the 

 changes in composition of the air passing through the lungs are very great, 

 so that this difference in assumed composition is not of as great magni- 

 tude as it is with other forms of apparatus. For example, air entering 

 the lungs may be assumed to contain 20.93 per cent of oxygen, and de- 

 terminations of the air leaving the lungs may show an oxygen content of 

 16.93 per cent, or a difference of 4 per cent. Consequently an error of 

 0.04 per cent in the assumed composition of the air entering the lungs 

 would only make an error of 1 per cent in the total oxygen determined. 



One of the most important and promising methods of studying the 

 respiratory exchange is that elaborated by Professor Jaquet of Basel, and 

 extensively used by both Staehelin 1 in Berlin and by Grafe 2 in Heidel- 



1 Staehelin and Kessner, Charite-Annalen, 1909, 33, p. 1. 



2 Grafe, Zeitschrift fiir physiologische Chemie, 1910, 65, p. 1. 



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