RESPIRATION 235 



to an altitude of 15,000 feet or over; yet we noted that a 23 per 

 cent saturation of the blood with carbon monoxide was tolerated 

 without inconvenience. One of the subjects was liable to head- 

 ache when his blood was saturated to 25 per cent or more with 

 carbon monoxide, but this was in no wise accentuated in these 

 experiments. That deficiency of oxygen was exerting its custom- 

 ary effect on the respiration is indicated by the low value of the 

 alveolar carbonic acid percentage. Both the subjects noticed dis- 

 tinct hyperpnoea for some time after commencing to breathe into 

 the respiration apparatus, and that this was accentuated on the 

 slightest movement. The face remained of a distinctly bluish 

 color throughout the experiment, but the blueness passed away 

 if the hyperpnoea became exaggerated for a short time by mus- 

 cular movement. On rebreathing normal air at the close of the 

 experiment well-marked Cheyne-Stokes breathing was once or 

 twice observed, indicating that the want of oxygen had induced a 

 real hyperpnoea which had lowered the general carbonic acid 

 pressure in the body considerably. 



In calculating the arterial oxygen pressures from the experi- 

 mental data of these experiments, it was necessary to make allow- 

 ance for the fact that the arterial blood was not fully saturated 

 with oxygen and CO, while the blood from the saturator must have 

 been almost completely saturated, as the oxygen pressure in the 

 air of the saturator was considerably higher, and hardly any CO 2 

 was present. For the correction required under these circum- 

 stances I must refer to our original paper. 



On looking at the results of the four experiments it will be seen 

 that in every case the arterial was above the alveolar oxygen pres- 

 sure. The mean difference seems to be outside the limits of experi- 

 mental error, but only amounts to 8 mm. 



A further series of experiments was made with the subject 

 doing muscular work. Preliminary experiments made with the 

 work done on a tricycle ergometer had shown that when the 

 breathing was greatly increased difficulties arose with the appa- 

 ratus. We therefore decided to make use of work with only one 

 arm. This enabled us to push the work to the point of fatigue, 

 when want of oxygen would be produced in the muscles, with 

 formation of lactic acid. That lactic acid was actually formed is 

 indicated by the low alveolar CO 2 percentages. The work appa- 

 ratus which we employed was of the simplest description. It 

 consisted of a lever which could be moved backwards and for- 

 wards, and transmitted its motion by means of a connecting rod to 



