THE BIOCHEMISTRY OF RESPIRATION 263 



If we admit the existence of organic peroxides in animal 

 tissues, it is evident that we accept to some extent the doctrine 

 of intramolecular oxygen. It is true that the actual quantity of 

 oxygen loosely bound up in the tissues in the form of peroxide 

 may be extremely small, but such as it is it corresponds to the 

 intramolecular oxygen of Pfluger and Hermann. Ehrlich x in 

 1885 made a number of interesting observations on intra vitam 

 straining which seemed to support the doctrine strongly. He 

 found that on injection of the somewhat stable alizarin blue into 

 rabbits, a few tissues such as liver and lung reduced it to alizarin 

 white, and so he concluded that they had a high degree of 

 oxygen avidity, or possessed very little store of intramolecular 

 oxygen. Other tissues, such as glands and some muscles, could 

 reduce the less stable indophenol blue to indophenol white, 

 whilst others, such as muscle of heart, tongue and diaphragm, 

 renal cortex and cerebral cortex, failed to reduce either pigment. 

 Hence he concluded that these tissues contained the largest 

 store of intramolecular oxygen. Corresponding to these results, 

 the writer found that all the tissues of this latter class are very 

 rich in indophenol oxidase {i.e. organic peroxide), whilst those 

 of the liver and lung class contain very little oxidase, and those 

 of the intermediate class intermediate amounts. It seems very 

 probable that there is some measure of truth in Ehrlich's 

 hypothesis, but no final conclusions can be arrived at until it is 

 found possible to estimate the exact share in the processes taken 

 by the reducing substances of the tissues. 



In addition to the insoluble indophenol oxidase, animal 

 tissues contain several soluble oxidases which appear to be 

 specific. The most striking of these is the uricolytic enzyme 2 

 or uricase which oxidises uric acid to allantoin and C0 2 . This 

 enzyme is present in considerable amount in the liver and 

 kidney of all the animals examined except those of man, from 

 which it is entirely lacking. Corresponding to this fact we find 

 that human urine does not contain a trace of allantoin, whilst 

 that of the dog contains most of its purin nitrogen in this form. 

 Uricase, like indophenol oxidase, is not assisted in its action by 

 peroxidase. It is not to be confounded with the oxidase, first 

 described by Horbaczewski, 3 which oxidises hypoxanthin and 



1 Ehrlich, Das Sauerstoff-Bedurfniss des Organismus, Berlin, 1885. 



2 Cf. W. Jones, Nucleic Acids, London, 191 4. 



3 Horbaczewski, Monatschr.f. Chem. 10, p. 624, 1889 ; 12, p. 221. 



