For =farm-houses=: subsoil drainage for slops, and a movable tank, with dry earth disinfection, for excreta. For =sea-side houses, isolated=: if there is vegetation, subsoil drainage for slops, and earth-closets. For =sea-side villages=: subsoil drainage and the pail system. For =sea-side houses=, where there is =no vegetation=: for excreta, earth-closets or a movable iron tank, with dry-earth disinfection; for slops, a water-tight cesspool, with arrangements for emptying its contents into the sea when the tide is ebbing. =How to prevent contamination of the air from the ground.= Have the house separated from the soil on which it is built by a layer of asphalt between two layers of cement, extending over the whole cellar-floor, through the foundation-walls and up above the point where the ground touches the walls outside. Or have the house built without a cellar, and with perforated underpinning, so as to allow a free circulation of air underneath it. The subsoil should also be drained by tiles laid at least a foot lower than the cellar-bottom. The cold-air boxes of furnaces should draw their supply from the external air. It is advisable to have a thin layer of cotton held in place by wire gauze to filter the air as it enters them. CHAPTER III. DISINFECTION. =How to prevent contamination of the air by the respiration, bodily emanations, and excreta of diseased persons.= It is not possible with our present knowledge to prevent the multiplication of morbid germs in the human body, when they are once implanted there, nor to prevent their discharge; but we can destroy them after their exit from the body, and so protect other persons who are not yet affected. The following instructions for the management of contagious diseases were prepared for the National Board of Health by Professors Chandler, Henry Draper, Barker, Vander Poel, E. G. Janeway, and Ira Remsen. _Instructions for Disinfection._ Disinfection is the destruction of the poisons of infectious and contagious diseases. Deodorizers, or substances which destroy smells, are not necessarily disinfectants, and disinfectants do not necessarily have an odor. Disinfection can not compensate for want of cleanliness nor of ventilation. I. _Disinfectants to be employed._ 1. Roll-sulphur (brimstone) for fumigation. 2. Sulphate of iron (copperas) dissolved in water in the proportion of one and a half pounds to the gallon; for soil, sewers, etc. 3. Sulphate of zinc and common salt, dissolved together in water in the proportion of four ounces sulphate and two ounces salt to the gallon; for clothing, bed-linen, etc. II. _How to use Disinfectants._