The =exciting cause= is a special micro-organism, the bacillus of Eberth. The contagion may be carried through the air from one person to another, but this is rarely the case. Though the water is the most common mode of conveyance, the bacillus has been found during epidemics in both water and milk. The water may be contaminated by the intestinal discharges which have not been properly disinfected. Extreme cold does not destroy the typhoid germs. Milk may be infected from the milk-can being washed with the contaminated water or the unclean hands of the milker. In fresh milk the germs multiply rapidly. Salads, celery, ice and fruits may be contaminated. Oysters have become infected while being fattened or freshened. It is thought by some that the poison is not eliminated from the sick in a condition capable of transferring disease to a healthy person, but must undergo changes in the soil before it is able to cause the disease in another. Typhoid fever may be caused, however, by direct contact with the stools. Filth, sewers, or cesspools do not directly cause the disease, but they form a suitable medium for the preservation of the typhoid germs. =Pathologically=, the characteristic lesions in typhoid fever consist of changes in the lymphoid elements of the bowels. These changes are most striking in the solitary glands and Peyer’s patches. The alterations which occur may be divided into four well defined stages: (1) =Infiltration=—the glands are enlarged from infiltration and there is marked cell proliferation, particularly Peyer’s glands in the jejunum and ileum and to a lesser extent those in the large intestine. The glands become pale and prominent. Occasionally the solitary glands, which are usually deeply imbedded in the submucosa, become prominent also. =Microscopically=, the capillary blood-vessels are at first considerably dilated, but later become more or less contracted, giving an anemic appearance to the follicles. The adjacent mucosa and muscularis may become infiltrated. The cells have the character of lymph corpuscles, some of which are larger, epithelioid in character, containing several nuclei. From the eighth to the tenth day this medullary infiltration reaches its height and then undergoes either resolution or necrosis. (1) =Resolution= takes place by a granular or fatty infiltration of the cells. This produces pitting of the swollen follicles, which may cause small hemorrhages.