RESPIRA TOR Y CHANGES IN AIR. 695 



The carbon dioxide is absorbed from the air by caustic potash, and a 

 constant supply of oxygen from the reservoirs is driven in, a manometer 

 in communication with the animal chamber indicating the pressure. 

 Samples of air for analysis can be drawn from the chamber, and thus 

 the part played by nitrogen determined, and a control placed upon the 

 completeness of the supply of oxygen and the removal of carbon 

 dioxide. Modified forms of Eegnault and Eeiset's apparatus have been 

 used by Hoppe-Seyler and Stroganow, 1 Pfliiger and Colasanti, 2 Schulz, 3 

 Seegen and Nowak. 4 



In Schaiiing's 5 respiration apparatus a constant stream of fresh air 

 was drawn through the chamber in which the animal was confined. A big 

 barrel served for the chamber, and air freed from carbon dioxide by 

 passing through Liebig's potash bulbs was aspirated through the appar- 

 atus ; on leaving the chamber the air passed through a flask containing 

 sulphuric acid, which removed the moisture, and through a weighed 

 potash bulb of huge size, of which the increase in weight gave the 

 amount of carbon dioxide expired by the animal. As a control, a sample 

 of air for analysis was removed from the barrel at the beginning and 

 end of the experiment. In this method the carbon dioxide alone was 

 determined, and the results were inaccurate, for the absorption was 

 incomplete, as is shown by the fact that the air leaving the bulbs 

 rendered lime water turbid. Many other forms of apparatus constructed 

 upon similar principles have been used. 6 



With the methods formerly in use it was impossible to maintain a 

 steady ventilation, and at the same time completely absorb the carbon 

 dioxide. To overcome this difficulty, Pettenkof er 7 introduced the 

 following modification. The total amount of air drawn through the 

 apparatus is measured by a meter ; continuous samples of the air 

 entering and leaving the chamber are steadily drawn through two 

 separate systems of absorption tubes and meters for the determination 

 of the moisture, carbon dioxide, and volume of the samples. The 

 difference in the amounts of water and carbon dioxide contained in the 

 two samples, multiplied by the total ventilation, gives the quantity of 

 moisture and carbon dioxide discharged by the animal. The intake 

 of oxygen is estimated in the following way. The animal is weighed at 

 the beginning and at the end of the experiment, and the difference 

 between the weights of carbon dioxide and water discharged, and the loss 

 in weight of the animal, represents the oxygen absorbed. Thus if W 

 represents the initial weight of the animal, and W\ its final weight, then 

 W - W l =w, the loss in weight of the animal. Let C0 2 + H 2 represent 

 the weights of carbon dioxide and water discharged during the experi- 

 ment, then C0 2 -hH 2 - w=0 2 , the oxygen absorbed. In thus estimat- 

 ing the oxygen, it is assumed that, apart from the carbon dioxide and 



1 Arch.f. d. ges. Physiol., Bonn, 1876, Bd. xii. S. 18. 



2 Ibid., 1877, Bd. xiv. S. 92. 



3 Ibid., Bd. xiv. S. 78. 



4 Ibid., 1879, Bd. xix. S. 347. 



5 Ann. d. Chem. u. Pharm., 1843, Bd. xiv. S. 214. 



6 Allen and Pepys, Phil. Trans., London, 1809, pt. 2, p. 412 ; Dulong, Ann. de chim. 

 et phys., Paris, 1841, Se"r. 3, tome i. p. 440; Despretz, ibid., 1824, tome xxvi. p. 337; 

 Boussingault, ibid., 18-14, SeV. 3, tome xi. p. 433 ; Journ. f. prnkt. Chem., Leipzig, 1845, 

 Bd. xxxv. S. 402 ; Senator, Arch. f. Anat., Physiol. u. wissensch. Med., 1872, S. 1 ; Lieber- 

 meister, Deutsches Arch.f. kliu. Med., Leipzig, 1870, Bd. vii. S. 75. 



7 Sitzungsb. d. k.-bayer. Akad. d. Wissensch. zu Munchen, math.-phys. CL, 1862, Bd. 

 ix. (2), S. 232 ; Ann. d. Chem. u. Pharm., 1862-63, Snpp. Bd. ii. S. 17. 



