RESPIRA TION. 531 



blood free from them. These results have been substantiated by the recent 

 researches of Bohr and Henriquez * on dogs ; these experiments have further 

 shown that a considerable portion of O may disappear as a result of processes 

 occurring in the blood during its passage through the lungs, and a large 

 amount of CO 2 be formed as one of the products. Thus they found that con- 

 siderably more O was absorbed from the lungs than could be pumped from the 

 blood, and that more CO 2 was given to the air in the lungs than was lost 

 by the venous blood. They believe that the tissues deliver to the blood par- 

 tially-oxidized substances which undergo a final splitting up when the blood 

 reaches the lungs. If this be so, the respiratory capacity of the blood, apart 

 from its capacity as a carrier of and CO 2 to and from the tissues, must be 

 considerably greater than indicated by Quinquaud's figures. 



The chief chemical product of the oxidative decompositions in the blood 

 and tissues is CO 2 ; but the quantity of O absorbed is not necessarily related 

 to the amount of CO 2 eliminated ; that is, during a given interval the quantity 

 of O may be out of proportion to the elimination of CO 2 , and vice versd. 

 Thus, in a muscle during rest, at normal bodily temperature, the consumption 

 of O is greater than the elimination of CO 2 , while during activity the propor- 

 tion of CO 2 to O increases and may exceed that of O. Rubner's 2 experiments 

 on the resting muscle at various temperatures accentuate the fact that the for- 

 mation of CO 2 may be independent of the quantity of O absorbed. Thus, at 

 8.4 the respiratory quotient was 3.28 ; at 28.2, 1.01 ; at 33.8, 1.18 ; and at 

 38.8, 0.91. The high respiratory quotient at low temperatures is to be 

 explained partly by direct oxidation and partly by intramolecular splitting, 

 which is independent of oxidation. It is probable that during rest O is util- 

 ized to some extent in oxidations which are not at once carried to their final 

 stage and in which relatively little CO 2 is formed ; hence during activity com- 

 paratively little O is required to cause a final disintegration of the now par- 

 tially broken-down substances, and thus to give rise to a relatively large 

 formation of CO 2 . (See Effects of Muscular Activity on Respiration and 

 Metabolism of Muscle, etc.) 



0. THE RHYTHM, FREQUENCY, AND DEPTH OP THE RESPIRATORY 



MOVEMENTS. 



The Rhythm of the Respiratory Movements. During normal breathing 

 the respiratory movements follow each other in regular sequence or rhythm. 

 Various instruments have been devised for the study of these movements 

 in man ; the form most commonly used is the stethograph or pneumo- 

 graph of Marey. The respiratory movements are communicated by a system 

 of levers to a tambour, thence through a rubber tube to a second tambour 

 having attached a lever which records upon a moving surface. In animals 

 a tracheal cannula or tube (p. 554) is usually inserted into the trachea, and 

 a tube is led from it to a recording tambour. In case the movements 



1 Comptea rendus, 1892, vol. 114, pp. 1496-99. 



2 DuBois-Reymond's Archivfur Physiologie, 1885, pp. 38-66. 



