CHAPTER XI 



CHEMISTRY AND PHYSICS OF RESPIRATORY EXCHANGES 



CONTENTS. Early notions of the importance of respiration (Aristotle, Galen, 

 Leonardo da Vinci, van Helmont, Boyle, Hook, Fracassati, Lower, Mayow). 2. 

 Modern doctrines (Black, Bergmann, Priestley, Lavoisier). 3. Theory of gas 

 exchanges in the lungs and tissues (Lagrange and Spallanzani, W. Edwards). 

 4. Extraction of gases from the blood (Magnus, L. Meyer, Hoppe-Seyler, Ludwig, 

 Pfliiger). 5. Varying content of arterial, venous, and asphyxiated blood. 

 6. State of the oxygen in the blood. 7. State of the carbonic acid in the blood. 

 8. Tension of gases in venous and arterial blood and in inspired >ancl expired air ; 

 theory of pulmonary gas exchange by diffusion and by secretory processes. 9. 

 Theory of gas exchanges in the tissues. 10. The respiratory quotient and its 

 variations. Bibliography. 



JUST as the Circulation provides for the exchange of fluid materials 

 between the blood and the tissues, so Respiration provides for the 

 exchange of gaseous materials between the environment and the 

 blood, and between the blood and the tissues. 



We have already seen that the function of respiration is 

 common to all living beings (see Chap. II. 4 ; Chap. III. 3). Even 

 Pasteur's anaerobes develop carbonic acid, utilising the oxygen 

 which is combined with the organic substances, and by its means 

 producing exothermic reactions, such, i.e., as the liberation of energy 

 in the form of heat. They thus fulfil the function of respiration, 

 albeit in a different way from other living beings, so that it cannot 

 be said that they do not breathe. The vast majority of living 

 creatures, however, respire free oxygen : the simplest organisms 

 directly; those which have circulating blood, indirectly, i.e. 

 through the oxygen of the blood. Among these last we dis- 

 tinguish external respiration, or the gas exchanges between the 

 environment and the blood, from internal respiration, or the gas 

 exchanges between the blood and the tissues. By means of the 

 first, the venous blood in the lungs and gills is rendered arterial ; 

 by the second, the arterial blood in the capillaries of the aortic 

 system or greater circulation is rendered venous. 



I. The phenomena of respiration first received a scientific 

 explanation in modern times, although they arise in physiological 

 processes that have a first claim on the attention of mankind. 



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