The mucous membranes are in constant contact with microörganisms and furnish conditions in many respects favorable for their rapid development. Nevertheless, the latter is interfered with and often inhibited by certain mechanical and chemical influences which afford protection. The conjunctiva is an extremely exposed membrane, which harbors, however, but a relatively small number of bacteria under ordinary circumstances. The tears before escaping from the conjunctival sac are sterile, and are probably saline enough to act as an antiseptic bath for the cornea. Moreover, by free escape of secretion through the nasal duct the conjunctival sac is kept constantly irrigated, to which is mainly due its ordinary healthy condition, as it is well known how commonly lesions follow obstruction to the lacrymal duct. The horrible results of Egyptian ophthalmia, _i. e._, the pyogenic form of conjunctivitis, are familiar to travellers in Egypt. Howe and others have shown that this disturbance is due to flies, which are carriers of infection, and are attracted toward the eyes of infants, while the superstitious notions of the parents restrain their children from instinctive protection of the eyes when thus irritated. There is probably no greater common carrier of pyogenic infection than the common house-fly, and nowhere is this agency more demonstrated than in the hot climates of the Orient. [Illustration: PLATE III FIG. 1 Artificial Dental Caries in Cross-section. Tubules Filled with Bacteria. (Miller.) FIG. 2 Putrid Tooth Pulp. Infection of Dental Tissue. × 1000. (Miller.) FIG. 3 Dental Caries. Disappearance of Dental Tissues as Result of Presence of Bacteria. (Miller.) FIG. 4 Dental Caries. Tubule Filled with Cocci. (Miller.) FIG. 5 Dental Caries. × 500. (Miller.) FIG. 6 Dental Caries. Tubules Plugged with Cocci. × 500. (Miller.)]