1. The problem of louse control by powders has been shown to be twofold, namely (a) to kill the lice present on a verminous person at the time of treatment, and (b) to prevent reinfestation of a deloused person or infestation of a clean person. In these experiments no single insecticide was found that would fulfil both functions.

2. The work shows the necessity of using laboratory tests (‘cell tests’) in conjunction with insecticide tests on the parasite living under natural conditions (‘field trials’).

3. The technique and results of the cell tests and the field trials are described in detail. In the field trials naturally louse-infested persons living in verminous surroundings were treated and examined daily to observe the true insecticidal value of each preparation.

4. Naphthalene was found to be the most effective insecticide for killing body lice quickly. It failed to give any protection against reinfestation.

5. The vegetable insecticides, derris and pyrethrum, were found to be toxic to Pediculns humanus corporis, but either alone or in combination with each other they were inferior to other combinations of insecticides.

6. The combination of high-boiling tar acids and derris resulted in the combined chemicals being more toxic to lice than either alone. This proved an activation effect, and the theory of activation is discussed.

7. Activated derris, while slow in killing lice, was shown to be the best preparation which gave protection against reinfestation.

8. The preparation referred to as A.L. 63 was outstanding as the best preparation that controlled body lice and which fulfilled the original conditions stipulated for a successful louse powder for human use. The formula is:

H.B.T.A. 2 %

Derris root 14·3 % giving 1 % rotenone and a minimum of 3 % extract in the final product

Naphthalene 50·0 %

China clay 33·7 %

The nature of each chemical in this formula is defined.

9. A.L. 63, when applied to the clothing of a verminous person, killed 95% of all lice on the treated garment in 24 hr., and gave complete protection against reinfestation for an average of 5 days, and partial protection for 8 days. When applied to clean garments as a prophylactic measure, A.L. 63 gave complete protection for an average of 7…8 days, and partial protection for approximately 16 days.

10. Patients living in a verminous environment were made to wear one shirt continuously for a month without washing it. Even under these conditions they were protected from infestation by treatment of the inside of the shirt, at 8-day intervals, with A.L. 63.

11. A short history is given of the use of A.L. 63 in the British army from 1940 to 1944.

During this work we have had much help and sympathy from many people, but we would like to place on record our especial thanks to the following: Prof. P. A. Buxton, of the London School of Hygiene and Tropical Medicine, for supplying us with the original material for establishing a louse colony, and for his great interest and encouragement during the work; Dr W. E. Parry, the Divisional Police Surgeon at Spitalfields, for his kindness in describing the best areas to search for suitable patients, and his assistance in finding suitable accommodation for establishing the ‘clinic’; those numerous volunteers, within the Cooper, McDougall and Robertson organization, who offered to feed lice when the colony was being maintained at the Research Station, and suffered much discomfort while doing so.