344 



Chemical Phenomena of Human Respiration, [June 20, 



current of air over pumice-stone moistened with a solution of potas- 

 sium hydrate, through the wide mouth bottle in which the titration 

 was being made ; by this means no atmospheric carbonic acid could 

 interfere with the correctness of the result. Fourteen pairs of analyses, 

 made to test the method, gave a mean difference of only 0"31 per cent. 



Two comparative experiments were carried out in a large air-tight 

 chamber in which a person lying in a deck-chair breathed first into 

 an india-rubber bag, representing the bell-jar, and next into the air of 

 the chamber. The air in the bag and in the chamber being subse- 

 quently analysed yielded practically the same weight of carbonic acid 

 expired within the same time.* 



The results obtained from the present inquiry are as follows : — 



1. The law of nature is further demonstrated that less air, reduced 

 to 0° C. and 760 mm. pressure, is breathed at high than at low altitudes 

 for the formation in the body of a given weight of carbonic acid. 



2. The known usual influence of food on the formation of carbonic 

 acid in the body is confirmed — the maximum amount expired occur- 

 ring between two and three hours after a meal, while the minimum is 

 before breakfast. 



3. The influence of food on the relation between the volumes of air 

 breathed (reduced) and the corresponding weights of carbonic acid 

 expired is clearly shown ; the volumes following, as a rule, the fluctua- 

 tions of the carbonic acid, but there is apparently a sudden change in 

 this relation at a period of between four and five hours after a meal, 

 when the carbonic acid expired falls proportionally faster than the 

 volumes of air breathed. The harmony of the tracings in one of the 

 charts accompanying my paper has recovered itself, however, over- 

 night, and the lines are again nearly parallel before the first morning 

 meal. In the other chart there are no experiments recorded made 

 before breakfast. 



4. The local state of the atmospheric pressure, as shown by the 

 barometer, has a marked influence on respiration, less air, reduced to 

 0° 0. and 760 mm. pressure, being taken into the lungs for the formation 

 and emission of a given weight of carbonic acid under loiver atmospheric 

 pressures than under higher pressures ; but this influence varies in 

 degree according to different persons. In the present inquiry when two 

 young men were experimented upon — in one case, for a fall of pressure 

 of 10 mm. (0*395 inch), there was a mean reduction of T076 per cent, 

 of the volume of air breathed for 1 gram C0 2 expired ; in the other 

 case, the mean redaction was greater, and amounted to 1*745 per cent. 



5. The above influence of local atmospheric pressures on the volume 

 of air breathed is not the same throughout the whole day, being much 

 less marked from two to four hours after a meal when the action of 



* In one experiment the difference amounted to 2'97 per cent. ; in the other to 

 06 per cent. only. 



