The direct origin of acute infectious diseases from the effluvia from drains or cesspools has occasionally occurred. Leaky and choked drains under a house are especially dangerous. The subsoil becomes contaminated more and more as time goes on; foul gases are aspirated into the house, owing to its interior being warmer than the subsoil; and finally infectious matter may find its way into the house, or carried by insects or vermin, through cracks in the earth. _Diphtheria_ has been ascribed to emanations from drains and sewers. There is reason to believe that a non-specific form of sore throat may originate in this way; but diphtheria is generally, if not always, spread by personal infection. _Diarrhœa_ has been occasionally ascribed to sewer-emanations. It chiefly occurs in hot weather, and is usually associated with a foul condition of the surface soil, and speedily ceases after this has been scoured by copious rain. _Enteric or typhoid fever_, has been frequently ascribed to drain and sewer effluvia. It was formerly thought that putrefactive changes alone, under certain conditions of temperature, etc., would produce it, and Dr. Murchison, one of the greatest authorities on the subject, who adopted this view, proposed for enteric fever the name “pythogenic fever” (_i.e._ filth-produced). Isolated cases of enteric fever, occurring where there is no system of drainage, support the same view, as does also the fact that, with the adoption of drainage, the enteric mortality has steadily diminished. On the other hand, numerous cases can be quoted to show that emanations from excreta have been breathed, and sewage-contaminated water drunk, for years, without the production of a single case of enteric fever—until a case is accidentally imported. The weight of evidence is clearly on the side of the view that only emanations from the liquid or solid dejecta of previous enteric patients will produce enteric fever, and that it is the solid particles of the urine or fæces, either inhaled as dust or carried on to food by flies, &c., or mixed with food by contaminated water, &c., which cause infection. Furthermore, modern investigation shows that infection by dust is the exception in England; and that the enteric infection is usually swallowed and not inhaled, being taken in infected water or milk or other food.