Certain species of insects (clothes-moths and granary insects) may be best destroyed by suffo cation in the fumes of carbon disulphide evaporated in shallow dishes placed at the top of the air-tight receptacle containing the ma terial to be fumigated. An ounce to 50 or 75 cubic feet is the usual proportion, the box being kept closed for twenty-four hours or more. Since the fumes of carbon disulphide are very explosive, lights must be kept away. Flydroeyanie-acid gas is also largely used to suffocate insects. espe •ially certain greenhouse and nursery stock pests, and the groups known as scale-inseets, notably the San Jos6 scale. The gas is generated from potassium cyanide (98-99 per cent. pure) in a of sulphuric acid and water, the propor tions being 1 oz. cyanide of potassium, oz. water. II!' oz. sulphuric acid for each 100 cubic feet for nursery stock operated upon; 125 cubic feet for trees, granaries, flour-mills, and rooms; and 2,50 cubic feet for greenhouses. The usual exposures are from half an hour to an hour for plants and trees, according to whether they are growing or dormant, and 12 to 24 hours for rooms, etc. Since both the gas and the salt from which it is made are virulent poisons, no person who is not both careful and competent should employ them.
The insects that attack domestic animals and man, though individually serious pests, form a numerically insignificant group when compared to the great group of plant-feeding species. Hogs and sheep may be freed from lice by greasy mixtures and tobacco or carbolic washes: in fested horses and cattle should be thoroughly curried once a week until the animals are free, the brush being dipped frequently in kerosene emulsion diluted with five or six parts of water. Similar remedies apply to the related parasites of the human subjeet, vaseline or lard being sub stituted for the kerosene emulsion. For the body-louse and the crab-louse hard boiling of infested ch4thes for half an hour or longer is essential. since the eggs arc very resistant. Poul try may he kept free from lice by a liberal supply of fine dust, and their houses by fumigation with carbon disulphide or hydrocyanic-acid gas once a week and the frequent application of kerosene and whitewash. Carbolic soap is a standard insecti cide against fleas in pet animals. With animals of all kinds, however, cleanliness is a great safe guard, since the insects which arrive first are de stroyed before they have a chance to breed.