RESPIRATORY EXCHANGE OF GAS. 819 



in the tissues in a short time without changing the quantity of oxygen contained 

 in the blood. The importance for respiration of such a property of the tissues 

 i.-^ evident; but it is perhaps too early to give a positive opinion on BOHR'S state- 

 ments and experiments. 



In regard to the carbon-dioxide tension in the tissue it must be 

 assumed a priori that it is higher than in the blood. This is found to 

 be true. STRASSBURG l found in the urine of dogs and in the bile a car- 

 bon-dioxide tension of 9 per cent and 7 per cent of an atmosphere, 

 respectively. The same experimenter has, further, injected atmospheric 

 air into a ligatured portion of the intestine of a living dog and analyzed 

 the air taken out after some time. He found a carbon-dioxide tension 

 of 7.7 per cent of an atmosphere. The carbon-dioxide tension in the 

 tissues is considerably greater than in the venous blood, and there is 

 no opposition to the view that the carbon dioxide simply diffuses from 

 the tissues into the blood according to the law of diffusion. 



Several methods have been suggested for the study of the quantitative 

 relation of the respiratory exchange of gas. The reader must be referred 

 to other text-books for details as to these methods, and we will here 

 mention only the chief features of the most important methods. It must 

 also be remarked, in regard to these methods, that those of REGNAULT 

 and REISET and of PETTENKOFER, determine the total gas exchange, 

 and indeed for a long time, while the three other methods determine the 

 respiratory gas exchange alone, and this only for a short time. 



REGNAULT and REISET'S Method. According to this method the animal or 

 person experimented upon is allowed to respire in an inclosed space. The carbon 

 dioxide is removed from the air, as it forms, by strong caustic alkali, from which 

 the quantity may be determined, while the oxygen is replaced continually by 

 exactly measured quantities. This method, which also makes possible a direct 

 determination of the oxgyen used as well as the carbon dioxide produced, has since 

 bfen modified by other investigators, such as PFLUGER and his pupils, SEEGEW 

 and NOWAK, and HOPPE-SEYLER, ROSENTHAL and OPPENHEIMER and especially 

 by ATWATER and BENEDICT. 2 



PETTENKOFER 's Method. According to this method the individual to be 

 experimented upon breathes in a room through which a current of atmospheric 

 air is passed. The quantity of air passed through is carefully measured. As it 

 is impossible to analyze all the air made to pass through the chamber, a small 

 fraction of this air is diverted into a branch line during the entire experiment, 

 carefully measured, and the quantity of carbon dioxide and water determined. 

 From the composition of this air the quantity of water and carbon dioxide con- 

 tained in the large quantity of air made to pass through the chamber can be 

 calculated. The consumption of oxygen cannot be directly determined in this 

 method, but may be calculated indirectly by difference, which is a defect in this 



1 Pfliiger's Arch., 6. 



2 See Zuntz in Hermann's Handbuch, 4, Thl. 2, and Hoppe-Seyler, Zeitschr. f . 

 physiol. Chem., 19; Rosenthal, Arch. f. (Anat. u.) Physiol., 1902; Zuntz and Oppen- 

 heimer, Arch, f . (Anat. u.) Physiol., 1905, and Bioch. Zeitschr., 14; Atwater and Bene- 

 dict, Bull, Dept. of Agriculture, Washington, 69, 109, and 136. See also Krogh, Wien. 

 Sitz. Ber., 115, III., and Skand. Arch. f. Physiol., 18. 



