Dysentery bacilli may survive in flies for as long as five days, and typhoid bacilli may similarily survive nearly seven days. This relates to the organisms in the flies intestinal tract, from which they are discharged in the excreta (fly specks) or by regurgitation, though on the external surface of the body their survival is brief.
Difficulties with flies can best be overcome by the elimination of their breeding place, namely manure piles. These if open and exposed should not be permitted to represent over a weeks accumulation. Stables should have tight floors and be well cleaned. The removal of manure at weekly intervals will re move the partially developed maggots therein and afford local relief, but however, merely transfer the difficulty to some other situation. Another, but more expensive method, involves the keeping of flies from manure by requiring its storage in fly tight bins or boxes. Another solution to this problem is afforded by the treatment of manure piles with substances which destroy the Substances must be used which are not too expen sive. Borax may be used at the rate of o.62 pounds of borax per 8 bushels of manure, but the treated manure may have an injurious effect on vegetation. Powdered hellebore, using one half pound to io gallons of water and applying this amount to each 8'bushels of manure is perhaps the most effective and prac tical substances to use for this purpose. Trapping and other wise catching the adult flies, particularly if practised at the beginning of the breeding season, is of distinct merit. Sticky fly paper and the swatter should be used in every home and eating house. Dwellings and eating houses should be screened, and food displayed at retail, particularly that eaten without further heating, should also be screened.
Traps of different kinds are in vogue, some of which are de signed to be placed near doors, where flies seek ingress, others over garbage cans or manure boxes, are all of value. Unless attention is paid to the breeding places however, traps are of slight service. Garbage accumulations should receive atten tion similar to manure.
The activity of flies as conveyers of infective agents from excreta gives opportunity to reiterate the importance of col lecting human excreta in privies that are of fly tight construction.
4. Insecticides.—Various methods are available for the de struction of insects within dwellings, buildings, vessels, and other enclosed spaces. Their destruction by gaseous poisons is the most satisfactory method, and is generally applied for the pur pose of destroying either the types which have a closer parasi tism, such as fleas, or bed bugs, or noxious types such as clothes moths, cockroaches, or vectors which may be present on the premises from which a case of plague, yellow fever, etc., has been removed and hence are potentially infected.
For this purpose either sulphur dioxid or hydrocyanic acid gas are commonly employed. The employment of gaseous in secticides demands that the quarters to be freed of insects be given the same preparation as that required for disinfection. When employed as an insecticide, it is not necessary that water vapor be employed with the burning sulphur, as anhydrous is effective. For this purpose two pounds of sulphur are re quired for each too° cubic feet of space. Crushed sulphur sticks or flowers of sulphur should be employed. The required amount of sulphur should be placed in a conical pile in a very shallow cast iron pot, which is supported on bricks in a tub of water. A small depression is made in the summit of the pile in which is placed a ball of waste or cotton saturated with alcohol. When all other preparations are completed the alco holic cotton is ignited and the operator immediately makes his escape. The quarters should remain closed for from 2 to 12 hours. The objectionable features of sulphur dioxid have been noted in the consideration of disinfectants.
A more satisfactory insecticide is hydrocyanic acid gas. It however is exceedingly poisonous to all mammals and man and should only be employed by one who is thoroughly competent and who fully understands its dangers. The gas is liberated from either sodium or potassium cyanid by means of sulphuric acid. Per too() cubic feet of the following proportion of these are required: K C N to oz. 1- oz.