210 SCIENCE PROGRESS 



Hypoxanthine is mon-oxypurine ; xanthine is di-oxypurine ; and 

 uric acid is tri-oxypurine. Any conditions that lead to the 

 increased katabolism of the cell nuclei, or any foods such as 

 sweetbreads or meat which are rich in nuclei or in purine 

 bases, will therefore lead to an increased formation of the 

 poisonous acid, and if the kidneys are unequal to the increased 

 strain of excreting it, the result is its accumulation in the body 

 and the production of the " uric acid diathesis." 



The question is not only of interest in itself, but the 

 mechanism of nuclear katabolism also illustrates a general truth 

 concerning the importance of the tissue enzymes. These may 

 be studied in extracts of different organs and tissues, and their 

 distribution varies a good deal ; but, speaking generally, those 

 which have to deal with uric acid formation are most abundant 

 in the liver and spleen. 



The first of these to act is called nuclease ; this liberates 

 from nucleic acid its two purine bases adenine and guanine, 

 each of which contains an amino- (NH 2 ) group. The next to 

 come into play are called de-amidising enzymes, because they 

 remove the NH 2 radicle; one of them termed adenase converts 

 adenine into hypoxanthine, another termed guanase converts 

 guanine into xanthine. Finally oxidases step in, which trans- 

 form hypoxanthine into xanthine, and xanthine into uric acid. 

 But even that does not bring the list to a conclusion, for in 

 certain organs {e.g. the liver) there is a capacity to destroy 

 the uric acid after it is formed, and so we are normally pro- 

 tected from a too great accumulation of this substance. What 

 exactly happens to the uric acid is uncertain, although it is 

 clear that the products of its breakdown are less harmful 

 than uric acid itself. The enzyme responsible for uric acid 

 destruction is called the uricolytic enzyme. The uric acid 

 which ultimately escapes in the urine is the undestroyed 

 residue. 



The question may next be asked, does our present know- 

 ledge of the chemistry of the nucleus assist us in any way 

 in understanding its behaviour during cell division. Here we 

 enter much more uncertain ground, and it may be frankly 

 confessed that at present we have no data for more than 

 guessing what are the chemical transformations which accom- 

 pany mitosis. There have, however, been theories put forward 

 by those who work at another branch of chemistry, namely 



