640 METABOLISM 



on the other hand, contains a nuclease capable of splitting the poly- 

 nucleotides into monomicleotides. The two pyrimidine nucleotides split 

 off do not undergo further change, but the purine nucleotides are con- 

 verted into nucleosides (the enzyme being designated "nucleotidase")- 

 Extract of the intestinal mucosa, besides having the same action as the 

 intestinal juice, can also decompose the purine, but not the pyrimidine 

 nucleosides, into carbohydrate and purine groups (specific action of 

 "nucleosidase"). A similar action is produced by extracts of kidney, 

 heart muscle, and liver. Blood serum, hemolyzed blood, and extract of 

 pancreas, on the other hand, are capable only of carrying the decompo- 

 sition as far as the mononucleotides. 



Eegarding the other enzymes mentioned in the above list, it is im- 

 portant to note that they appear at different stages in embryonic develop- 

 ment, and that their distribution varies considerably in different species 

 of adult animal, the spleen, liver, thymus, and pancreas containing them 

 most abundantly. The distribution of enzymes in the organs of the 

 monkey resembles that in the lower animals considerably more than it 

 does that in man. Some remarkable facts have come to light regarding 

 guanase and adenase, particularly that guanase is deficient in the organs 

 of the pig, in the urine of which animal it has also been found that the 

 purine bases are in excess of the uric acid. This absence of guanase 

 no doubt accounts for the fact that deposits of guanine may occur in the 

 muscles, and that these may be so large as to constitute the condition 

 known as guanine gout found in this animal. Adenase, on the other 

 hand, is absent from the organs of the rat, which again corresponds with 

 the fact that, when adenine is injected subcutaneously into these ani- 

 mals, it undergoes oxidation without the removal of its amino group. 

 In the human organism, adenase appears to be absent from all of the 

 organs, whereas guanase is present in the kidney, lung and liver, but 

 not in the pancreas or spleen. Xanthine-oxidase exists only iri the liver. 



The distribution of uricase is perhaps the most interesting. It is pres- 

 ent in most of the lower animals. On account of its presence extracts 

 of the liver, spleen, etc., in all breeds of dogs, with the exception of 

 Dalmatians, rapidly destroy uric acid; and practically no uric acid 

 when injected subcutaneously can be recovered unchanged in the urine, 

 but appears as allantoine. Uricase, however, is absent in man. This has 

 been demonstrated by finding (1) that when uric acid is injected sub- 

 cutaneously, nearly all of it appears in the urine, and (2) that uric acid 

 is not destroyed when extracts of the organs are incubated at body 

 temperature with uric acid or its precursors. It must of course be kept 

 in mind that, although the uric acid is thus shown not to be destroyed 

 in vitro, it may nevertheless be destroyed in the living animal. 



