INTERCHANGE OF GASES. 239 



excretion of that gas in a similar manner. Nevertheless, the respiratory 

 interchange of gases is a chemical process. 



According to v. Fleischl the concussion to which the venous blood is subjected 

 on being pumped into the pulmonary arteries provides for a more ready escape of 

 the carbon dioxid, a point that is of the greatest importance with respect to the 

 respiratory process. 



The absorption of oxygen from the alveolar air for the purpose of 

 oxidation of the venous blood in the pulmonary capillaries is a chemical 

 process, as the gas-free hemoglobin in the lungs takes up oxygen to 

 form oxy hemoglobin. That this absorption depends, not on diffusion 

 of the gases, but on the atomic combination pertaining to the chemical 

 process, is shown by the fact that the blood does not take up more 

 oxygen when the pure gas is respired than when atmospheric air is 

 respired; further, that animals that are made to breathe in a small, 

 closed space will absorb into their blood all of the oxygen but traces, to 

 the point of suffocation. If the respiratory absorption of oxygen were 

 a diffusion-process, much more oxygen would have to be taken up in the 

 first case in accordance with the partial pressure of the gas; while in 

 the latter case such an extensive absorption could not take place. 



FIG. 90. Pulmonary Catheter. 



Even in highly rarefied air (high balloon-voyages) the absorption of 

 oxygen remains independent of the partial pressure. However, in a 

 space containing rarefied air a longer time and a more vigorous shaking 

 are required for the absorption of oxygen by the blood at the tempera- 

 ture of the body; that is, the absorption of oxygen is not diminished, 

 but is retarded. In this way is explained the death, for example, of the 

 aeronauts Sivel and Croce*-Spinelli, during an ascension to a height 

 where the atmospheric pressure is only one-third the normal. 



The laws of diffusion come into play in connection with the absorption of 

 oxygen only to the extent that the oxygen, in order to reach the red 

 puscles, must, first of all, diffuse into the plasma, where it immediately ente: 

 chemical combination with the erythrocytes. 



The excretion of carbon dioxid from the blood into the alveolar 

 air could also be well represented in the form of an equalization of 

 sion (diffusion) ; but here again chemical processes are operative al 

 they have not yet been investigated in many details, 

 of oxygen by the erythrocytes produces at the same time an expulsioi 



