OXYGEN SUPPLY. 53 



The choice of the two methods of admitting oxygen, i. e., from a 

 weighed cylinder or through a meter, depends upon the facilities of the 

 laboratory and the limits of its finances. If a weighed cylinder is used 

 it is necessary to have at least two small cylinders which can be alter- 

 nated or else one small and one large cylinder from which the small 

 one can be refilled occasionally. The equipment necessary for the 

 use of a meter comprises a good barometer, a 1-liter Bohr meter, a 

 glass jar large enough to immerse the meter, a small oxygen cylinder 

 for calibration purposes, and a large cylinder for general supply. Most 

 experimental laboratories where respiration work is carried on are 

 equipped with barometers, so that the additional equipment actually 

 required would ordinarily be the Bohr meter and glass tank and a 

 large supply of oxygen. After a meter is once installed and properly 

 calibrated it should remain in good condition indefinitely, although 

 occasional calibrations should be made. One meter has been in use 

 in this laboratory for 6 months without calibration and when it was 

 recalibrated by an operator who had had no experience with it, the 

 results agreed to within 1 per cent of the correction factor which had 

 been in use previously. It should be stated that in this case the meter 

 was taken out of the bath and the water in it removed; the meter was 

 then refilled, put back into the tank, and re-leveled before calibration. 



The use of a meter involves more calculation in obtaining the results 

 of experiments than the use of a weighed cylinder, but a cylinder 

 requires the additional time of weighing which practically offsets the 

 increase in calculations. Accordingly, so far as time is concerned, 

 there is no advantage in either case. In general, it would appear 

 from the experience in this laboratory with cylinder and meters that 

 the use of the latter is preferable because there is less likelihood of the 

 loss of the determination of oxygen with the use of the meter if the 

 proper method of admission is used and ordinary precautions are taken. 



ZUNTZ-GEPPERT METHOD. 1 



The successful use of the Zuntz-Geppert method in this investigation 

 is largely due to the courtesy of Professor Zuntz. During a stay of 

 several weeks in the Institute of Animal Physiology at Berlin, I had the 

 privilege of acquiring the technique of this method under the immediate 

 supervision of Professor Zuntz, and wish here to express my thanks for 

 the assistance rendered me at that time and for the many helpful 

 points obtained pertaining to the study of the respiratory exchange. 



DESCRIPTION AND USE OF PARTS OF APPARATUS. 



A detailed description of the mouthpiece and nose-clip, the valves, 

 and the various parts of the sampling and gas-analysis apparatus is 

 given in the following pages. The general principle employed in the 

 Zuntz-Geppert method of determining the respiratory exchange is 



1 Magnus-Levy, Archiv f. d. ges. Physiol., 1894, 55, p. 11. 



