422 Dr. AT. Marcet, [Feb. 10. 



In M. David's ease so much irregularity is observed as to the 

 amount of carbonic acid expired in connexion vrith the food taken, 

 that it is rot possible to draw any inference as to the direct influence 

 food exerted in this respect. He informs me he considers his digestion 

 so slow that he does not bathe (in the bake of Geneva) till three and 

 a half or four hours have elapsed after a meal. 



Influence of the Temperature of the Atmosphere on the Amount of Car- 

 honic Acid Expired. — This influence was sharply defined, even for 

 small differences in the temperature of the air. and it was found that 

 at the same station as the atmosphere became warmer, the amount of 

 carbonic acid expired fell precisely in an equal proportion. The first 

 series of experiments on myself at Yvoire were made on the 27th and 

 2^th of August : the temperature of the air was still high, and the 

 mean reading of the thermometer in the shade during the experiment, 

 was 69 r- 9 F. On that occasion, a mean of 504 mgrrns. carbonic acid 

 was found to be expired by myself per minute, at a mean period of 

 2 h. -46 m. after a meal. A second series of experiments upon myself 

 at that same station was undertaken on the 20th, 21st, and 22nd 

 October, yielding; a mean of 5 72 mgrms. carbonic acid expired per 

 minute ; autumn was setting in. and the atmospheric temperature 

 had fallen to a mean of GO" '3 at the time of the experiments; these 

 were made at a mean period of 2 h. 35 m. after a meal, or nearly the 

 same as in the first series. The circumstances attending the two series 

 of experiments were therefore similar, with the exception of the at- 

 mospheric temperature, which was lower by 9~"6 on the second than 

 on the first occasion. It is very interesting to observe, that the 

 carbonic acid in the second series is just what might have been 

 expected, if in an inverse proportion to the temperatures, these pro- 

 portions being calculated would yield 0*493 grrn.. which is very 

 nearly 0'504. or 0*5 S4 mgrm.. which is very nearly 0'573. If we 

 now consider the experiments made on myself at Courmayeur, before 

 ascending to the Col. they will be found to yield 494 mgrms. of 

 carbonic acid with an atmospheric temperature of 76" T. while the 

 second series, undertaken on returning to Courmayeur. after our 

 stay on the Col du Geant. gave 492 mgrms. at a mean temperature 

 cf 77°. the mean time the experiments were made after food being 

 2 h. 43 m. in one case, and 2 h. 29 m. in the other. In this instance, 

 the mean temperature varies by less than 1\ and the carbonic acid 

 expired is also as near as possible the same. 



AL David's two series of experiments at Courmayeur. at a mean 

 time of 2 h. 58 m. and 3 h. 34 m. respectively after a meal, gave for 

 the first 727 mgrms. carbonic acid, with a mean atmospheric tempera- 

 ture of 71"2. and for the second, after our return to Courmayeur again, 

 727 mgrms. carbonic acid, with a mean temperature of 72~"2. these 

 figures harmonising in a remarkable degree. 



