430 



Dr. W. Marcet. 



[Feb. 10, 



not in that of M. David. This result in M. David's case in no way 

 invalidates the well-known influence of the ingestion of food as 

 increasing the amount of carbonic acid expired, but is apparently due 

 in a great measure to the comparatively small number of experiments, 

 and to circumstances connected with a slow rate of digestion. 



2. The influence of the temperature of the atmosphere on the 

 amount of carbonic acid expired was well marked in both cases ; the 

 mean weights of carbonic acid expired at Courmayeur (3,945 feet) by 

 both of us being the same respectively at the mean temperatures 

 observed, which were equal in both series ; but it was found that the 

 amount of carbonic acid expired at the same station varied inversely 

 with the change of temperature ; the readings observed ranged from 

 60° -3 to 77° (Col du Geant not included). 



3. For a difference of altitude of 2,715 feet between 1,230 feet 

 and 3,945 feet, and a relative atmospheric humidity lower by 

 about 31 per cent, for the higher station (70 per cent, at Tvoire), the 

 mean weight of carbonic acid expired by each of us, reduced to the 

 same temperature was found to be in excess at the higher over 

 the lower station by 8*6 per cent, in my case and 8"3 per cent, in 

 M. David's. This shows clearly the influence of altitude coupled 

 with increased atmospheric dryness towards promoting combustion in 

 the body. 



4. The sudden change from a lower and very warm place to a very 

 high and cold station, with a barely adequate diet and insufficient 

 training, was productive on the present occasion of a decreased forma- 

 tion of carbonic acid in both of us, and a feeling of want of power to 

 react against the external cold. 



5. The amount of carbonic acid expired by each of us was not the 

 same. M. David, a younger man than I am, gave out a total mean 

 of 27'6 per cent, more carbonic acid than I did, calculating this excess 

 from the carbonic acid we expired per minute reduced to equal tem- 

 peratures ; and moreover the excess exhibited much regularity at each 

 station respectively. The mean surplus, without reduction for tem- 

 perature, would have amounted to 30 "9 per cent. 



6. A smaller weight (volume reduced) of air is breathed within a 

 given time in the mountains, at altitudes which may vary with different 

 persons, than in the plains or low valleys, although the actual volume 

 of air expired be larger under a lower barometrical pressure; and, 

 moreover, a smaller weight of air is required by the body to produce 

 within it a given weight of carbonic acid at certain elevations than 

 near the sea level ; this confirming my results obtained on former 

 occasions. 



7. At an elevation of 11,030 feet above the sea, and a mean tem- 

 perature of 41°- 7 and 43° '4s for each of us respectively, the rate of 

 breathing was accelerated in both our cases, though rather less in mine 



