Williams, in Idaho, found the greatest number of cases in winter had been fed hay made from alfalfa (lucerne) and timothy, though some had small grains and native grasses. The soil was dry, porous, gravelly, devoid of humus, and lying on lava rock. The altitude and clearness of the atmosphere were supposed to exclude the idea of cryptogams, yet the crops generally were raised by irrigation. The water was from clear mountain streams. Stables were generally low and full of manure, with thatched roofs, but hardly tight enough to be called close. In these cases the defective stable room, the irrigation, the leafy hay (lucerne), and the probable presence of ferments (bacteria), are the only suggestive conditions. In a fatal outbreak which I saw among the Wilkesbarre, Pa., pit mules, rain-soaked and badly fermented timothy hay, overwork in view of a strike, and a Sunday’s holiday in an unshaded yard under a hot July sun, in contrast with the previous darkness and coolness of the pits, coincided to disturb the general health. In several of the Southern States it is attributed to worm-eaten corn. Trumbower thinks it should be traced to the parasitic fungi that grow on plants, grains, and vegetation. In many instances the disease has appeared simultaneously with the feeding on certain specimens of brewer’s grains, oats and hay, so that to use Trumbower’s words these were the carriers if not the prime factors of the disease. In recognizing how much cryptogams and bacteria vary under different conditions of life, and what various products they elaborate at different stages of their growth, we can theoretically explain the absence of the disease at one time and its presence at another under what seem to be identical circumstances, as also the variety of symptoms shown in different outbreaks. While this causation cannot be said to be absolutely proved, it is not antagonistic to the facts in many of the best observed outbreaks, and may serve as a hypothetical working theory until actual demonstration can be furnished. The affection suggests a narcotic poison introduced from without, rather than a disease due to a germ propagated in the system. This need not, however, exclude the operation of attendant conditions such as overwork, plethoric feeding, excitement, close stables, heat exhaustion, etc., which tend to bring about cerebro-spinal congestion. Even the electric tension of Idaho, of the United States generally, and of Egypt, in connection with their comparatively dry atmosphere, should not be overlooked in considering the possible causative factors. In all probability as we learn more of the true pathology of the disease, we shall come to recognize not one, but several toxic principles, and several different affections each with its characteristic phenomena in the somewhat indefinite affection still known as cerebro-spinal meningitis.