We must recall, too, that a certain moiety of the purins derived from nuclein metabolism lags in the _lymph_ spaces and _lymphatics_, and this, as Walker Hall reminds us, must reduce the quantity present in the blood-stream at any one time. Also, as the same authority reflects, the lymph stream being probably richer in _sodium ions_ than the blood, the entry of the nucleins therein may be retarded and so lead to a still further reduction of the blood content. There is yet another possibility, he reminds us, viz., “that the purin content of the blood varies in the peripheral pulmonary hepatic and osseous streams, and that, while in some parts the purins are being carried to the kidneys for excretion, in others they are being transported from one organ to another for further metabolism.” For, as before pointed out, the enzymes responsible for the ultimate disruption of the _nucleosides_ are scattered in different organs, and Walker Hall suggests that “a transport of half metabolised nucleotides from one organ to another may form a part of the normal processes of nuclein metabolism.” This may well lead us on to consider the limitations that beset even the most modern tests in use for uric acid determination. _Disabilities of Modern Tests._—With all its outstanding advantages, even the Folin method of uric acid estimation has its drawbacks. As Curtman and Lehrman have pointed out, different workers have, even on _identical blood samples_, arrived at results which vary widely. Nor, disconcerting though it be, do the limitations of this mode of hæmo-analysis cease here. Thus we know from Gudzent and Apolant that the soluble but unstable biurate is constantly being transmuted into an insoluble stable type, in other words, metamorphosis from one _isomer_ into another. But, unhappily, the tests to hand fail of differentiation of the several _tautomeric_ forms of uric acid. Also, as isomers of uric acid actually exist, then _quâ_ Walker Hall, why not isomers of _purins_ and _pyrimidins_ also? But here again our tests are insufficiently eclectic. They give us no clue as to the affinities or blends of purins or pyrimidins for or with other substances. Again, as our criteria fall short of identifying the exact form of the “purin combinations” it follows, therefore, that they tell us nothing as to whether “the increase is due to a more active transport of purins from one organ to another for further metabolism or simply to a transport to the kidneys for elimination.”