834 SPECIAL- PHYSIOLOGY. 



hand, contains more oxygen and less carbonic acid, as shown by the 

 following table. (Magnus.) 



Oxygen. Carbonic Acid. 



100 vols. of Venous blood, . . 5 vols. . .25 vols. 

 100 vols. of Arterial blood, . . 10 vols. . . 20 vols. 



It has also been found that the proportions of oxygen and carbonic 

 acid in venous blood returning from muscles at rest, are 7.5 and 31, 

 and from muscles in action, 1.265 and 34.4 ; whilst in arterial blood 

 the proportions are 17.3 of oxygen and 24.2 of carbonic acid. (Sczel- 

 kow.) According to Magnus, arterial blood contains twice as much 

 oxygen as venous blood generally, whilst, in the special case of the 

 blood from muscles, the proportion is at least 2.3 to 1. Again, ordi- 

 nary^ venous blood contains th more carbonic acid than arterial, and 

 that from muscles at rest, about Jth more. 



The interchanges of oxygen and carbonic acid between the air and 

 the blood, which characterize respiration, have, through the researches 

 of Dalton, Draper, and Graham, received a partly physical and a partly 

 chemical explanation. The elimination of urea and uric acid by the 

 kidneys, and of certain excretory ingredients of the bile, is accom- 

 plished by organic vito-chemical processes performed by certain spe- 

 cial epithelial cells; but the absorption of oxygen by, and the elimina- 

 tion of .carbonic acid from the lungs, or other respiratory organ, are 

 purely physical and chemical processes. These may, indeed, be imi- 

 tated artificially out of the body ; for, as already mentioned, if a moist 

 bladder be filled with venous blood and be suspended in atmospheric 

 air or oxygen, the surface of the blood in contact with the bladder soon 

 becomes scarlet, and, during that change, oxygen is absorbed, and 

 carbonic acid is given out from it through the moistened bladder. It 

 is remarkable that a function of the animal economy, so immediately 

 and constantly necessary to life, is removed from the contingencies 

 surrounding & purely organic process, and is brought into the sphere 

 of physical and chemical actions. It is also worthy of remark, that 

 the physical processes which accomplish the escape of the deleterious 

 carbonic acid gas from the blood, and mix it with, the air, also aid in 

 the entrance of the essential purifying and stimulating oxygen from 

 the air into that fluid. The processes in question are the diffusion of 

 ga&es, or the tendency of dry gases to diffuse into each other, and their 

 mutual diffusion when in a dissolved condition. 



It was shown by Dalton, that, even when a light gas, such as hydrogen, is 

 poured into a glass jar on to the surface of a heavy one, such as carbonic acid, 

 or when a bottle full of the light gas is inverted over another bottle containing 

 a heavy gas, with their mouths applied to each other, the gases do not remain 

 stationary, but are mutually transported into each other against gravity until 

 they have intermixed in certain definite proportions. The facility" with which 

 they intermix is such, as to have been expressed by the phrase that each gas 

 offers no more resistance to the other than would an actual vacuum. This 

 simple intermixture is called the diffusion of gases ; it takes place with a defi- 

 nite energy, irresistible and invariable, when the conditions exist for its exer- 

 cise. The force with which it takes place, and its extent in any particular in- 

 stance, are said by Dalton to be generally inversely as the densities or weights 

 of the two gases respectively. Subsequent experiments on a most extended 



