THE CHEMISTRY OF RESPIRATION 



1103 



Magnus, in Heidenhain's laboratory, that the blood passing to the lungs 

 contained more carbonic acid gas and less oxygen than that passing away 

 from the lungs. The effects of this discovery were to transfer the chief seat 

 of oxidation to the tissues of the body, and to show that the blood acts 

 simply as a carrier of the oxygen from the lungs to the tissues, and of the 

 carbon dioxide from the tissues to the lungs. We thus learnt to distinguish 

 between external and internal respiratory processes. A consideration of the 



FIG. 505. Barcroft's modification of the Topler pump. 



chemical mechanisms, involved in the process of external respiration, in- 

 cludes therefore an investigation of the manner in which gases are held by 

 the blood and of the factors which are responsible for the transfer of oxygen 

 and carbon dioxide from blood to alveolar air, and from alveolar air to blood. 

 If blood be exposed to a Torricellian vacuum at the ordinary tem- 

 perature, the whole of its contained gases is given off. For the purpose of 

 extracting the blood gases, a great variety of pumps have been devised. In 

 every case a glass vessel is evacuated by means of the mercury pump, and 

 is then put into connection with a reservoir containing blood which has been 

 defibrinated, or has been prevented from clotting by the addition of oxalate 



