514 Dr. W. Marcet on the Function of Respiration at [Apr. 24, 



creased at tlie middle station, rmdergoing a marked and sndden reduc- 

 tion at the seaside. 



Water Expired from the Lungs at the Various Stations, 



The third part of my paper refers to the moisture exhaled. 



It was apparent at the outset that a falling off in the atmospheric 

 pressure, from rising above the sea, would be attended with a corre- 

 sponding increase of evaporation from the lungs, and a proportional 

 cooling effect on the respiratory organs. The apparatus used for the 

 inquiry was disposed as follows : — 



A tube drawn out at both ends was loosely filled with fragments of 

 calcic chloride ; it was large enough to ensure the absorption of 

 the whole of the vapour expired in three minutes. One end of the 

 tube was connected with one of my large india-rubber bags, while the 

 other end had a ring of vulcanised india-rubber fixed round, to which 

 the mouth was applied. A delicate spring valve (by Coxeter) was 

 fitted into the neck of the tube next the bag, and was weighed with 

 the tube ; it effectually prevented any admission of air into the tube 

 except that given out from the lungs. Either the tube or the bag 

 was placed in communication with a water gauge by a neck and india- 

 rubber tubing. Every now and then the calcic chloride was tested as 

 to its power of retaining all the moisture ; this was done "by con- 

 necting another similar tube with it and weighing it after breathing 

 through them both. No mouthpiece was used in these experiments, 

 as moisture was found to deposit on anything interposed between the 

 mouth and tube. The air breathed was inspired through the nose 

 only while the whole of the air expired was driven through the 

 tube, the nose being kept closed with the thumb and index. I found 

 no difficulty in doing this with accuracy ; great care was taken 

 to keep the saliva from flowing into the tube together with the 

 air expired. Except in the case of a few experiments at the summit 

 of the Peak, I alone submitted myself to this part of the inquiry. 

 The experiments were made by series of usually three at a time, the 

 figures given in my table are the means of those of the different 

 series. 



The numbers actually obtained gave, of course, the weight of the 

 moisture evaporated from the lungs, together with that of the atmo- 

 spheric humidity of the air exhaled; a correction had, therefore, to be 

 made. I determined the atmospheric humidity by means of dry and 

 wet bulb thermometers, and the corresponding weight of moisture in 

 a given bulk of air was taken from Glaisher's hygrometrical tables 

 (fifth edition). 



The results from these experiments have been condensed in the 

 following table : — 



