The question then arises as to what becomes of that moiety of the _food purins_ which fails to appear in the urine as _uric acid_. Now the amount of allantoin that appears in the urine is negligible. Moreover, Ackroyd, having shown that the organism cannot destroy allantoin, it is possible that the minimal amounts excreted thereof in the urine are all derived from the food. Accordingly, if, as experimental feeding with _purins_ or _nucleic acid_ appears to indicate, purins are destroyed in the body they “pass through some other route than allantoin, and possibly, that part of the purin which is destroyed does not pass through the stage of uric acid.” Such is Wells’ opinion, and he reminds us that _in vitro_ the destruction of uric acid can be attained by other routes than through allantoin. Thus, it can be broken down into glycocoll, ammonia, and CO₂, or by another method of disintegration it furnishes first alloxan (C₄H₂N₂O₄), then parabanic acid (C₃H₂N₂O₃), which in turn yields oxalic acid and urea. But while it is probable that there is more than one way in which uric acid can be decomposed in the body, nevertheless there is, according to Wells, no evidence that either of the alternative routes above suggested is ever affected in the animal body. In this _impasse_ Siven suggests the further possibility, viz., that the moiety of the food-purins which fail of recovery from the urine undergo partial destruction in the intestine by _bacteria_. Stewart, however, in his “Physiology,” discussing _uricolysis_, maintains that a considerable destruction of uric acid and other purin bodies goes on in the body and mainly in the _liver_. He reminds us that when uric acid is heated in a sealed tube with strong hydrochloric acid, it breaks down into glycin, carbon-dioxide and ammonia, and he maintains that “there are grounds for believing that a similar decomposition takes place in the body, and that the products are then transformed into urea in the _liver_”; this, through the agency of a special ferment called the _uricolytic enzyme_. Also, Flack and Hill, discussing the metabolism of _nuclein_, hold that some of the uric acid thus formed may be transmuted into urea by an uricolytic ferment present in the _liver_, muscles, and _kidneys_. This same agent they consider “probably destroys a considerable amount of the uric acid formed in the body. Indeed, uric acid, even when given in the food, owing to the presence of this enzyme, causes no increase in the uric acid output of the body.”