BESPIRA TION. 4 1 9 



that the transmission of O between the alveoli and the blood cannot be satis- 

 factorily explained by mere diffusion. Moreover, about twice as much argon 

 exists in solution in the blood plasma as can be accounted for by physical 

 laws. 



Facts of this kind are explicable on the hypothesis that the living tissues 

 are, as contended by Ludwig, Bohr, and others, actively engaged in the proc- 

 ess, but our knowledge is as yet too incomplete and contradictory to justify 

 its acceptance. Until, therefore, we are in possession of the results of further 

 research we are justified in the belief that the interchange of and ( !< ). 

 between alveoli and blood is due to physical and chemical factors, diffusion 

 being most important, and that it may be possible that the living tissues take 

 some active part. 



The Forces Concerned in the Interchange of O and C0 2 between the 

 Blood and the Tissues. — Innumerable facts show that the chief seat of the 

 chemical processes in the body is in the tissues, and that the decompositions 

 are essentially of an oxidizing character whereby C0 2 is formed as one of 

 the most important effete products ; consequently the blood as it is carried 

 through the capillaries gives up O and receives C0 2 . 



Experiments show that the tissues exert a strong reducing action, and that 

 their avidity for O is so great that they will take it up at extremely low 

 pressures. Moreover, never more than mere traces of O can be obtained 

 from the tissues, because the gas upon its absorption immediately enters into 

 chemical combination. 



The tension of 0O 2 in the tissues is considerably higher than in blood. 

 Strassburg, 1 in a loop of intestine into which he injected atmospheric air, found 

 that the tension was 58.52 millimeters of Hg, which is considerably greater 

 than in either arterial or venous blood. Thus we find that the tension of O in 

 the tissues is nil, owing to the avidity with which substances of the tissues 

 combine with the gas, and its chemical fixation; while that of ( ( ), is very 

 high. Comparing the tensions of these two gases in the blood and the 

 tissues, it will be observed that there are present conditions which arc highly 

 favorable to the passage of () to the tissues and of CO a in the reverse direction : 



o. CO,. 



Tensions in arterial blood 29.64 21.28 



Blood-vessel walls 



Tensions in tissues 0.00 



y.b4 S5J.28 



f i 



0.00 58125 



It is manifest from the above that O should pass from the blood to the tissues, 

 and C0 2 from the tissues to the blood. 



The lymph is probably merely a passive medium in this interchange. It 

 contains, according to Ham marsten, only traces of O, from 37.5 to 17.1 vol- 

 umes per cent, of C0 2 , and from 1.1 to 1.63 volumes per cent, of N. The 

 mean percentage of C0 2 is lower than in serum, but Gaule has shown that the 

 tension is higher. Doubtless the same relations hold good for the plasma and 



1 Lor. cit. 



