A determination of indol and indican is often of the greatest value, both in determining the extent of infection and the presence of pus. Indol is set free under the following circumstances: (_a_) Suppuration in a closed cavity. (_b_) Continued suppuration in a cavity with an outlet. (_c_) Ulceration or necrosis of tissue. The degree of indicanuria will depend on the length of time pus has been present, the possibility of absorption from the tissues surrounding it, and its degree. When pus is fully formed in a serous sac the indican reaction becomes intense according to the length of time pus has been present. This is particularly true in the empyemas of childhood. In continued suppuration with a free outlet the production of indol will be great; but the amount finally eliminated will depend upon the character of the surrounding tissue. When solid tissue, like bone, becomes affected, the elimination of indol is intense. Rapid biogenic degeneration of tissue causes an increased amount of indol to be deposited in the liver, and it is possible at postmortem, by simple extraction with absolute alcohol, to take from the liver this excess deposit in the shape of its oxidation product, indigo blue. Lardaceous degeneration is characterized by marked and persistent elimination of indol, which seems to be a product of tyrosin. It occurs frequently in the liver, in which indol is notably deposited. Its primary factor is deposited by the blood, in which latter indol circulates and is oxidized. Lardaceous material gives a red or blue color with oxidizing agents, which latter yield with indol an indigo red or blue.