W. J. Mallory, critically analysing Ackroyd’s cases, points out that he used only _hypoxanthine_ in his studies; also that, while _hypoxanthine_ has this advantage, that it is of definite and known chemical composition, furnishing a known quantity of basic nitrogen, it labours under this drawback: “It is by simple oxidation converted into uric acid, and probably calls into action only a limited part of the ferment system concerned in the formation of uric acid.” As a consequence, therefore, the amount of information on metabolism that can be gleaned through its usage is more restricted than if _nucleinic acid_ were invoked in its place; for this substance, on the other hand, calls into action all the various enzymes concerned in the disruption of nuclein or nucleic acid. Alive to these advantages, Mallory, in addition to hypoxanthine, used _nucleinic acid_ in his investigations of purin metabolism in a series of eight “undoubted cases of so-called rheumatoid arthritis.” The value of the inclusion of nucleinic acid is revealed by the fact that some of the cases, when given exogenous purin in the form of _hypoxanthine_, showed no deviation from the normal. On the other hand, when given _nucleinic acid_, a prolongation of the period of increased uric acid excretion ensued; this even though the total amount of basic nitrogen in nucleinic acid is less than in hypoxanthine. Thus 4 grams of nucleinic acid have 0·2632 gram of basic nitrogen, while 0·75 gram hypoxanthine has 0·309 gram of basic nitrogen. Apart from his own series of cases, Mallory analysed those of other observers, and his conclusions are as follows: “Of nineteen cases of rheumatoid arthritis in which the purin metabolism has been studied by three different observers, nine cases, or 47·3 per cent., show a marked variation from the normal in their reaction to purin-containing substances while they are on a purin-free diet. “In these cases the period of increased uric acid excretion which follows the administration of purin-containing substances is much _prolonged_. Following the administration of purin-containing substances, a considerable number of cases suffer from attacks of _sub-acute arthritis_, accompanied in some cases by an increased uric acid excretion.” It will be seen that in virtue of:— (1) The prolongation of the period of exogenous uric acid excretion, and (2) Increased uric acid excretion during attacks of sub-acute arthritis, certain cases of _rheumatoid arthritis_ manifest a certain resemblance to gout, though, as Mallory remarks, “other features characteristic of that disease are lacking.”