554 



THE RESPIRATORY EXCHANGE 



oxygen and oxidising various substances. Schmiedeberg found 

 that blood alone produces no appreciable oxidation of benzyl 

 alcohol (H 6 C 5 CH 2 OH) and aldehyde of salicylic acid 



.COIL 



PA 



\)H 



but if the blood containing one or other of these substances is 

 made to circulate through a freshly excised kidney, considerable 

 quantities of benzoic acid (C 6 H 5 C0 2 H),-or of salicylic acid 



\)H 



as the case may be, are produced. 



A better method than Ludwig's is the examination of samples 

 of the arterial blood entering and of the venous blood leaving an 

 organ in the living animal ; here the conditions approach more 

 nearly the normal, and the respiratory exchange of the organ 

 can be investigated under different general or local conditions. 

 In this way the effect of the contraction of a group of muscles 

 upon the gaseous contents of the blood which flows through them 

 has been investigated by various observers : the percentage of 

 oxygen in the venous blood is much diminished and the carbon 

 dioxide is increased, notwithstanding the increase in the volume 

 and velocity of the blood which circulates through the active 

 muscles. The following table gives the results of such experiments 

 made by Sczelkow, Chauveau and Kaufmann, Hill and Nabarro.( 27 ) 



