ELIMINATION OF CARBONIC ACID. 825 



eral or comparative experiments ; because the same person does not, 

 under such conditions, breathe equally, at all times, even after con- 

 siderable practice ; nor can different persons breathe equally, in re- 

 gard to each other, differences in the depth and duration of the respi- 

 rations rendering a comparison of the results fallacious. 



For these reasons, observations have been made on men and ani- 

 mals, placed in suitable hermetically closed chambers, and able to 

 breathe with less, or even no restraint. The breathing -chamber com- 

 municates with the air by means of a small supply tube on one side, 

 and on the other is connected by a tube with an aspirator, i. e., a 

 second closed chamber filled with water ; according as this water is 

 permitted to flow from the aspirator, air is withdrawn from the breath- 

 ing-chamber, whilst fresh air enters by the supply tube. To insure 

 the absence of carbonic acid, from the air employed, the supply tube 

 has a bend in it, containing a solution of caustic potash. The tube 

 connecting the breathing-chamber with the aspirator, has also a bend 

 containing asbestos, moistened with concentrated sulphuric acid, for 

 the absorption of the exhaled water ; besides this, it is fitted with a 

 Liebig's potash-tube, for fixing and weighing the carbonic acid formed 

 in respiration, and also with another bent tube, for again desiccating 

 the remaining air. By such an apparatus, the quantity of air passing 

 through the air-chamber, and the quantity of carbonic acid produced 

 in any given time, can be determined. (Dulong and Despretz's ex- 

 periments on Animals.) In observations on men, the body has been 

 inclosed in a second smaller box, so that the head alone projected into 

 the air-chainber ; the products of cutaneous respiration and exhala- 

 tion are thus separated from the pulmonary respiration and exhala- 

 tion, the gases and vapor given off by the skin being retained in the 

 smaller box, and those given off by the lungs being discharged into 

 the breathing-chamber. (Scharling's and Hannover's experiments on 

 Man.) By others, the face alone has been covered with a tight-fitting 

 mask, through which a stream of air enters by two valved openings, 

 and from which it is drawn off through a tube into a receiver, by 

 means of an air-pump. (Andral and Gavarret.) Instead of supplying 

 the breathing-chamber, in which animals have been placed, with pure 

 atmospheric air, known quantities of oxygen, proportioned to the quan- 

 tity of carbonic acid formed, have been introduced. The arrange- 

 ments necessary for the gradual absorption of the carbonic acid and 

 the introduction of fresh oxygen, render this apparatus somewhat 

 complex, but interesting results have been obtained by it. (Regnault 

 and Reiset.) In long-continued experiments, however, the quantity 

 of nitrogen in the chamber gradually increases by exhalation from the 

 animal's lungs ; hence the atmosphere breathed by it is no longer nor- 

 mal, and the respiration is modified accordingly. 



The experiments of Pettenkofer and Voit, undertaken with the 

 pecuniary assistance of the late King of Bavaria, are still more elabo- 

 rate, costly, and complete. A large closed breathing-chamber is pro- 

 vided, in which the person experimented upon can live and breathe 

 for many hours, as easily as in an ordinary apartment; and through 

 it, copious streams of air, as much as 75 cubic metres per hour, are 



