16 
may have hatched out before they become large enough to lay any eggs. 
As the gas is explosive it should be used in a tight case and kept away 
from sparks or fire. More recently a more satisfactory agent has been 
discovered, a mixture of three parts by volume of ethylene dichloride 
(C 2 H 4 CI 2 ) with one part of carbon tetrachloride (ChCl 4 ). Its advan- 
tages are “being highly toxic to insects, non-explosive, non-inflammable, 
non-toxic to man unless highly concentrated and breathed for protracted 
periods, non-injurious to specimens, inexpensive, and easily applied" 
(Leechman, 1931, 135-136). 
Gassing methods are necessarily impracticable in the field, except in 
a small way where specimens may be placed in covered tin cans, etc. The 
methods of fumigating large specimens are treated in the following pages 
(page 74). 
DDT as an Insecticide 
DDT (dichloro-diphenyl-trichloro-ethane) is the most outstanding and 
the most widely used of the newer insecticides. The compound was dis- 
covered in 1874, and rediscovered as an insecticide about 65 years later, 
becoming extremely effective in combatting insect vectors of disease during 
the latter part of World War II. Its extraordinary effectiveness against 
many species and its prolonged residual action, its formulation, application, 
and the precautions that should attend its use have been well publicized in 
technical and popular articles (See References, Gibson and Twinn, Supple- 
ment by Twinn, 1946; Twinn, 1945, 1946, 1947; Twinn and Balch, 1946). 
Twinn (1945) states: 
“DDT is classed as a poison, but can be used safely if applied and handled with 
proper precautions, as outlined in the containers in which the product is sold. Contact 
of the skin with oil solutions should be avoided as much as possible, as DDT can be 
absorbed in this form. It is advisable to wash exposed parts of the person with soap 
and water after any considerable use of oil solutions or concentrated emulsions . . . 
DDT in any form should be kept out of foodstuffs, a recommendation which applies to 
any insecticide. In the dry form, such as in powder formulations, DDT is safe to handle, 
but persons using it should avoid inhaling or swallowing the dust. Tying a handker- 
chief across the nose and mouth is a good precaution. 
“Insecticides offered for sale in Canada have to be registered in accordance with 
the provisions of the Pest Control Products Act. Under the regulations of this act 
the ingredients, guarantees, purposes of the product, directions for use, and the text of 
labels of such insecticide materials are reviewed by competent officials of the Depart- 
ment of Agriculture before applications for registration are accepted. Mention of this 
is made to assure the public that proprietary preparations containing the new insecti- 
cide DDT may be purchased and used with confidence, in accordance with the claims 
of the manufacturer or vendor shown on the labels of such products.” 
Mr. C. H. Rayley, Textile Research Laboratory, Division of Chemistry, 
National Research Council, Ottawa, writes {in litt., 1947) : 
“It (DDT) is coming into wide use as an agent for protecting wool garments and 
fabrics from attack by the webbing clothes moth and the carpet beetle . . . The 
material is usually applied in the form of a solution in some organic solvent, either by 
spraying or dipping. However, it should be pointed out that in the case of specimens 
which may have become infected, it may be necessary to arrange for a fumigation of 
the entire specimen, using some toxic gas, since spraying the outside of the specimen 
would not kill the insects in the interior. In such cases a combination of fumigation 
and spraying should be effective . . . The toxicity of DDT when used in the quantities 
required to protect perishable specimens would not be expected to be appreciable. 
Actually DDT was used during the war for the impregnation of garments worn next 
to the skin for the purpose of controlling lice”. 
