826 SPECIAL PHYSIOLOGY. 



drawn, by means of a double pump worked by a small steam-engine, 

 the total quantity passed through being accurately registered, after 

 desiccation, by a gas-meter interposed between the chamber and the 

 pump. Atmospheric air is admitted to the chamber by proper aper- 

 tures, and the amount of carbonic acid gas and water already contained 

 in it, is accurately determined. The contaminated air leaves the cham- 

 ber by two tubes, one passing from near the ceiling, and the other 

 from near the floor, which then join a common tube ; this tube leads 

 into a desiccating box, from which the dried air passes through the 

 gas-meter to the cylinders of the double air-pump. To absorb and 

 measure the whole of the carbonic acid gas contained in this large 

 stream of air, the total product of the respiration of the person living 

 in the chamber, would be an inconvenient process ; accordingly, a 

 small portion of the contaminated air is diverted for that purpose, 

 through an analyzing apparatus, into which this portion of the air is 

 drawn by a peculiar suction- and pressure pump, moved by the steam- 

 engine which works the larger pump. This portion of air passes in 

 succession through an apparatus which absorbs and measures, first the 

 water, and then the carbonic acid contained in it, and afterwards 

 through a desiccating box and small gas-meter, by which it is ulti- 

 mately measured. Its quantity, compared with the larger quantity 

 drawn through the main tube, furnishes the means of calculating the 

 total quantity of carbonic acid eliminated by the person confined in 

 the breathing-chamber, in a given time. The quantities of carbonic 

 acid gas and water, formed by the combustion of a stearin candle in 

 the chamber, may be determined by this apparatus as correctly as by 

 the ordinary process of organic analysis. 



Dr. E. Smith has employed a small mask, which fits tightly over the 

 mouth and nostrils, and is provided with a valved inlet and outlet. 

 The air is inspired through, and measured by, a spirometer, consisting 

 of a delicate gas-meter. The expired air passes through a desiccator, 

 containing sulphuric acid to absorb watery vapor; then through a 

 gutta-percha box, divided into many chambers and cells, containing 

 caustic potash, and offering a surface of 700 square inches, so as to 

 abstract the carbonic acid ; and, lastly, through a second desiccator to 

 retain any moisture carried off and lost, from the potash box. The 

 increase in weight of the mask, with the connecting-tube and first 

 desiccator, shows the amount of vapor exhaled from the lungs ; whilst 

 the addition to the joint weight of the potash box and the second desic- 

 cator, gives the weight of the carbonic acid expired. 



Regnault and Reiset, Pettenkofer and Voit, and Dr. Edward Smith, 

 have endeavored to determine not merely the amount of carbonic acid 

 eliminated in ordinary breathing, but also the influence of those condi- 

 tions which modify that amount, and likewise have attempted to obtain 

 data for comparing the quantity of carbonic acid formed and of oxy- 

 gen taken in, with the animal heat evolved. 



Some only of the results obtained by various observers, can here be 

 quoted. Dumas, calculating that by an adult male, of average size, 

 320 cubic inches of air are respired in one minute, and that this con- 

 tains, on expiration, 4 per cent, of carbonic acid, concluded that about 



