During the following two years, two more exhibits related to hospital supplies and sanitation were added to the rapidly developing Hall of Health exhibition which was opened in 1924. A third exhibit in 1925 consisted of 96 mounted color transparencies illustrating services provided by hospitals to promote public health. Plans for the further development of the Hall of Health continued during 1926, and contacts were made with organizations interested in the educational aspects of the healing arts. As a result, several new exhibits were added. In 1926, the American Optometric Association helped in the installation of an exhibit on conservation of vision or the care of the eyes under the slogan "Save your vision," as a phase of health work. Other exhibits in the Hall at this time were: what parasites are; water pollution and how to obtain pure water; waste disposal; ventilation and healthy housing, and the importance of recreation; purification of milk and how to obtain pure milk; transmission of diseases by insects and animals; how life begins; prenatal and postnatal care and preschool care; duties of the public health nurse; and social, oral and mental hygiene. With the acquiring of more medical appliances and the widening of the scope of the exhibits, more and more space was needed, and attention was turned to the area of the medical gallery which had been occupied by the _materia medica_ collection for almost four decades. To gain more exhibit space, it was decided that the greater part of the crude drugs should be removed from the exhibits and be kept as a reference collection and for research.[13] [Illustration: Figure 6.--EXHIBIT ON EGYPTIAN AND HEBREW MEDICINE, installed about 1924, which was illustrated by graphs and drugs mentioned in extant records of this ancient period. (Smithsonian photo 30796-C.)] [Illustration: Figure 7.--EXHIBIT ON MEDICAL HISTORY during the Greco-Roman period. (Smithsonian photo 30796-D.)] [Illustration: Figure 8.--EXHIBIT ON REMEDIES DERIVED FROM DRUGS of vegetable origin, displayed about mid-1930's. (Smithsonian photo 30439.)]