In _leukæmia_ protein-destroying forces are at work, and the urine contains large quantities of _uric acid_. The same is attributed to the formation and destruction of enormous numbers of _leucocytes_, but the urinary findings in this respect have been extremely variable. While increased uric acid elimination has been vouched for by many authors, some have noted increase in the _purin bases_, sometimes with, and sometimes without increase in the uric acid; while others again have even noted a decrease in uric acid and _phosphoric acid_ excretion. Apart from these contradictory findings, it would appear, according to Magnus-Levy, that in _acute_ leukæmias the relation between the number of leucocytes and the uric acid output is most variable. Lastly, the different types of leukæmia present differences in regard of their uric acid output, the increase in the _myelogenous_ variety being much more marked than in the _lymphatic_ form. Wells, discussing these conflicting data, considers that they are but the reflex of the “known fluctuations in the course of the pathological processes of leukæmia; the number of leucocytes, the size of the lymphatic organs, and the general condition of the patient all vary greatly from time to time, often with remarkable rapidity and the excretion of products of metabolic activity must vary likewise.” Continuing, he observes that the enormous increase in the amount of lymphoid tissue in the body and blood must give rise to a greatly augmented _nuclein katabolism_, with sequential appearance of _uric acid_, _purin bases_, and _phosphoric acid_ in the urine. This he holds to be well demonstrated by the increased elimination of uric acid and purin bases, together with a general increase in the nitrogen output such as has been frequently noted in sequence to the therapeutic use of X-rays in leukæmia, this attributable to the increased autolysis known to be induced by X-rays. As to this question of the relationship of _leucocytosis_ to _uric acid excretion_, it must be borne in mind that the number of leucocytes and the excretion of uric acid do not always vary directly. Parallel studies of the blood and urine have shown that _leucocytosis does not invariably accompany increased uric acid excretion_. Indeed, Hutchison and MacLeod have recorded cases of _leucopenia_ without any reduction in the amount of uric acid eliminated. Also, we have to recall that on a _purin-free_ diet the amount of endogenous uric acid is more than can come from _nuclein_ destruction in the body. As suggested by Burian, some may be derived from the _hypoxanthine_ in muscular tissue. In short, while nuclein disintegration is the outstanding source of endogenous purin, yet, for the reason cited, it cannot be regarded as the sole source, for the exact origin of all the endogenous purin is not as yet established.