28 Dr. Thomas Thomson [Jan. 



found that the most unexpected alterations are observable 

 in the same individual, though he be in perfect health, 

 and though he make no sensible alteration in his mode of 

 living. 



During the course of the month of May, 1832, 1 analyzed 

 air from my own lungs on ten consecutive days, between 

 eleven and twelve o'clock each day. Before stating the 

 results, it may be proper to mention the method of analysis 

 employed. I procured a glass tube, capable of holding 

 about three cubic inches of air, and about half an inch 

 in diameter. It was shut at one end and open at the 

 other. This tube being filled with mercury, and placed 

 inverted on a mercurial trough, I introduced into it about 

 two and a-half cubic inches of air from my lungs, taking 

 care, in the first place, by making half an expiration 

 through a narrow glass tube, to expel all the common air 

 from the trachea and mouth, and also from the tube, by 

 which it* was conveyed to the eudiometer. The surface of 

 the mercury in the tube was then marked by tying round 

 it a sewing thread, and the whole was left till the air 

 ceased to contract. Then a quantity of moderately strong 

 potash ley was introduced, and the whole was left un- 

 touched for twenty-four hours. The diminution of bulk of 

 the air was then carefully marked, by tying a sewing 

 thread round the tube at the new surface of the mercury. 

 I then filled the tube with mercury, up to each of the places 

 marked by the sewing threads, and weighed each portion 

 of mercury. The difference between the two weights, gave 

 the diminution of bulk sustained by the air, by the absorp- 

 tion of its carbonic acid. I then calculated, what the bulk 

 of the air and of the carbonic acid gas absorbed would have 

 been, at the mean pressure and temperature; making 

 allowance for any change in the height of the barometer 

 and thermometer, which took place during the interval. 

 I ought to observe, however, that during the ten days of 

 these experiments, both the barometer and the thermometer 

 were tolerably steady. 



The following table exhibits the volume of carbonic acid 

 gas, in 100 parts of the air expired from my lungs during 

 each of the ten days, at 11 o'clock a. m. : — 



