The question of the value of wearing a gauze mask over the mouth and nostrils during an influenza epidemic is still an open one. Masks, however, have been found useful in protecting against some other diseases of respiratory origin. In December, 1917, Weaver (40) reported favorably on the use of gauze masks in the Durand Hospital of Infectious Diseases. The masks were used by nurses in attendance upon patients with contagious diseases, and also by patients who were convalescing from diphtheria, meningitis or pneumonia and who were in the same wards with those having other respiratory diseases. In a later article Weaver (41) stated that by the use of masks they had been able to reduce the percentage of diphtheria carriers among their nurses in the diphtheria wards to 5.2 per cent., as compared to the average of 23.25 per cent. during the 20 months immediately preceding their adoption of their use. He recommended the general use of masks for physicians when in contact with all types of respiratory diseases. In March, 1918, Capps (39a) reported encouraging results in the control of infections through the masking of all patients at Camp Grant. During the epidemic the wearing of masks became quite general, and was very popular in many sections. Several sets of laboratory experiments have been carried out recently to determine whether the masks are of practical value or not. The experiments have generally consisted in spraying cultures of living bacteria over sterile bacterial plates which were protected by one or more layers of gauze. A number of variations were made in the manner in which this was done: (a) the distance between the nozzle of the spray and the mask was varied, and the distance between the plate and the mask kept constant; (b) the distance between the plate and the mask varied, and the distance between the nozzle and the mask kept constant; (c) the use of masks both over the nozzle of the spray and over the plate being kept constant, and the distance between the two masks varied. In a somewhat different set of experiments the mask was placed over the mouth of a person, who was told to talk or cough over an agar plate, and the bacterial plate being held at various measured distances from the face. By counting the number of colonies which developed upon the plates it was possible to get fairly reliable data as to the efficiency with which the bacteria were intercepted by the gauze. Weaver (42) found that if enough gauze was used, it would filter out all of the bacteria passing from the spray in the direction of the plate. The efficiency of the mask being in direct proportion to the fineness of the mesh and the number of layers employed. Doust and Lyon (43) made a series of experiments to determine the distance through which droplets are carried when expelled under different circumstances. They found that in ordinary speech infected material is projected for about four feet, and that during