The more fortunate of human beings need never concern themselves with the chemical history of uric acid. It is always present in their body-fluids. It is excreted by the kidney. Its formation is of no greater interest than that of creatinin and other nitrogenous compounds which escape the almost universal reduction to urea. Persons who have a uric acid diathesis are in a very different plight. Every scrap of evidence bearing upon its origin is of supreme importance. Unfortunately, the evidence collected as yet is scanty, and its application for remedial purposes impracticable. The only disease in which uric acid is invariably in excess is leucocythæmia. This is a condition or habit marked by the presence in the blood of a very great number of white blood-corpuscles and a paucity of red ones. The connection between this disease and the production of uric acid is made plain by certain experiments in diet. If flesh which contains relatively a large proportion of cell-nuclei is eaten, the uric acid excreted is markedly increased. Sweetbread, especially “neck sweetbread”—_i.e._, thymus gland—is a mass of comparatively small cells with large nuclei. If thymus gland be substituted for all other meaty foods, the quantity of uric acid appearing in the urine is doubled. A large increase in the quantity of ordinary meat or fish consumed also increases uric acid, because all meat-fibres contain nuclei. If egg-albumin be taken instead of meat, uric acid is not increased. A sudden excess of muscular work leads to an increase in uric acid, owing presumably to the unusual activity of the tissues. This used to be very noticeable in the case of young men during the first few days of “training” under the old system; but it may have been due to the generous consumption of chops and steaks, rather than to the increase in physical work, and consequent destruction of tissue. Nuclei contain nucleo-proteins, which split into proteins and nuclein. Chemically, it is reasonable to attribute to nuclein the parentage of uric acid; a plausible line of descent can be traced. The association of leucocythæmia with the production of uric acid is probably due to the destruction of leucocytes which are present in abnormal numbers (_cf._ p. 53).