During the year from May, 1898, to May, 1899, 26 male and 28 female patients in the Derby County Asylum were attacked with the disease variously known as dysentery, dysenteric diarrhoea, or colitis, and characterised clinically by bloody stools and rise of temperature, and in advanced cases showing in post-mortem examination extensive thickening and ulceration of the lower end of the large intestine, with numerous microscopic hæmorrhages into the submucous layer. Of the 54 attacked, 23 died, in 13 the colitis being apparently the direct cause of death, in 10 a contributory cause. Some brief notes of our attempt to ascertain the cause of the outbreak may be of interest, though the results obtained were mostly negative or inconclusive.