THE BIOCHEMISTRY OF RESPIRATION 265 



enzymes. This may be because the protein and other tissue 

 constituents with which the oxidases are inevitably mixed 

 inhibit their activity, but it is natural that a doubt should arise 

 as to whether the oxidases are really responsible for the main 

 oxidation processes which occur in living organisms. In order 

 to obtain further information on the subject, the writer 1 has 

 made a number of comparisons of the respiratory powers and 

 oxidase content of living tissues treated in various ways, in 

 order to see how far they correspond. The experiments were 

 made with freshly excised rabbits' kidneys, which can readily be 

 perfused with oxygenated saline solution, and the gaseous 

 metabolism of which can be estimated by analyses of the gases 

 in the inflowing and outflowing saline. It was found that on 

 exposure of kidneys to high temperature their respiratory 

 powers and their oxidase content were destroyed to about the 

 same extent. After half an hour in saline at 50 C. both were 

 reduced to about half their initial value, whilst at 53 they were 

 reduced to a fifth, and at 55 to about a tenth their value. Again, 

 on perfusion of kidneys with saline containing o*i to 04 per cent, 

 of lactic acid, or 1 per cent, of phenol, both respiration and 

 oxidase were destroyed to about the same extent ; but other 

 poisons acted less destructively on the oxidase of the tissues 

 than on their respiration. With chloroform the difference 

 observed was moderately great ; with mercuric chloride and 

 ammonia more considerable, whilst with formaldehyde it was 

 greatest of all. For instance, perfusion with 0*3 per cent, form- 

 aldehyde did not affect the oxidase at all, whilst it reduced the 

 respiration to a seventh the normal. Perfusion with 0*5 per 

 cent, formaldehyde destroyed 40 per cent, of the oxidase, but 

 92 per cent, of the respiratory power. Even more striking than 

 this is the effect of mincing up the kidney tissue and keeping it 

 two days. Its respiratory powers are thereby entirely lost, 

 whilst its oxidase content is unaffected. There seems to be an 

 unstable linkage of some kind in the chain of oxidation processes 

 which is readily destroyed by poisons and in other ways, with- 

 out the oxidases being necessarily affected at all. Perhaps this 

 linkage is a lipoid membrane which binds together enzyme and 

 substrate, and so permits the normal oxidation processes of the 

 tissues to proceed. Thus the writer 2 found that on perfusing 



1 Vernon, J own. Physiol. 44, p. 150, 191 2. 

 - Vernon, ibid. 45, p. 197, 191 2. 



