Pyrethrum, whale oil (in the form of soap), fish oil (in the form of soap), soft soap, paraffine, Prussic acid, Paris green, white lead, sulphur, carbon bisulphide, acorus calamus, camphor, Cayenne pepper, tobacco, snuff, asafetida, white hellebore, eucalyptol, quassia, borax, acetic ether are most important substances used as insecticides, alone, or in combination of two or more of them. The Prussic acid and Paris green are dangerous poisons and require to be used with extreme care:

Insect powder is used for all small insects and as a destroyer of roaches. The observations of some experimenters seem to show that the poisonous principle of these flowers is non-volatile, but the most favorable conditions under which to use them are in a room tightly closed and well warmed. There may be two poisonous principles, one of which is volatile. Disappointment sometimes arises in their use from getting powder either adulterated, or which has been exposed to the air and consequently lost some of its efficiency.

The dust resulting from the use of insect powder sometimes proves irritating to the mucous membranes of the one applying the powder. This is best avoided by the use of a spray atomizer.

Persistence in the use of any means is an important element in the work of destroying insects. A given poison may be employed and no visible result follow at first, when in reality many may have been destroyed, enough being left to deceive the observer as to numbers. They multiply very rapidly, too, it must be remembered, and vigorous work is required to combat this increase. Where they can easily migrate from one householder's premises to those of another, as in city "flats," it requires constant vigilance to keep them down, and entire extermination is scarcely to be expected.

The ordinary insect powder on the market is made from pyrethrum carneum, pyrethrum roseum, and pyrethrum cinerarise-folium. The first two are generally ground together and are commercially called Persian insect powder; while the third is commonly called Dalmatian insect powder. These powders are sold in the stores under many names and in combination with other powders under proprietary names.

The powder is obtained by Brushing the dried flowers of the pellitory (pyrethrum). The leaves, too, are often used. They are cultivated in the Caucasus, whence the specific name Caucasicum sometimes used. Pyrethrum belongs to the natural order compositŠ, and is closely allied to the chrysanthemum. The active principle is not a volatile oil, as stated by some writers, but a rosin, which can be dissolved out from the dry flowers by means of ether. The leaves also contain this rosin but in. smaller proportions than the flowers. Tincture of pyrethrum is made by infusing the dried flowers in five times their weight of rectified spirit of wine. Diluted with water it is used as a lotion.

Borax powder also makes a very good insectifuge. It appears to be particularly effective against the common or kitchen cockroach. Camphor is sometimes used, and the powdered dried root of acorus calamus, the sweet flag. A mixture of white lead with four times its weight of chalk is also highly recommended. The fish-oil soaps used in a powdered form are made from various recipes, of which the following is a typical example:

Powdered rosin...... 2 pounds

Caustic soda........ 8 ounces

Fish or whale oil..... 4 ounces

Boil together in a gallon of water for at least an' hour, replacing some of the water if required.

The following insect-powder formulas are perfectly safe to use. In each instance insect powder relates to either one of the pyrethrum plants powdered, or to a mixture:

I

Insect powder. ... 8 ounces av. Powdered borax. . 8 ounces av. Oil of pennyroyal. 2 fluidrachms

II

Insect powder. ... 8 ounces a v.

Borax........... 8 ounces a v.

Sulphur......... 4 ounces a v.

Oil of eucalyptus. 2 fluidrachms This formula is especially good for cockroaches:

III

Insect powder. ... 14 ounces av. Quassia in fine powder........ 6 ounces av. White hellebore, powdered...... 2 ounces a v.