The treatment of pneumonia by chemical compounds of known composition specifically adapted to inhibit the growth and the activity of the pneumococcus is a recent development of therapeutics. Quinine and its modifications were among the first of such drugs to be tried. In 1917 Moore and Chesney1 and in 1919 Solis-Cohen2 employed the quinine derivative ethylhydrocupreine hydrochloride in the treatment of pneumonia with some degree of success. This success was offset, however, by the toxic action of the drug on the visual apparatus. Maclachlan and his associates,3 in a study of a number of modifications of quinine prepared for them by the Mellon Institute of Pittsburgh,4 found experimentally that one of these—namely, hydroxyethylapocupreine—had a high pneumococcidal activity both in vitro and in mice and did not cause blindness. Subsequently, Maclachlan and his associates3 reported its beneficial effect clinically in a number of cases of pneumonia.