Dangerous Blood

The time may come when animals (including humans) will be able to poison the bugs that bite them. Last week the U.S. Department of Agriculture was hard at work on this project. Many modern insecticides have only a slight effect on warm-blooded creatures. An animal whose blood is spiced with some such deadly substance should make an unattractive meal for lice, ticks or mosquitoes.

The most successful experiments were with human body lice, which normally live on human blood. When work began at Agriculture's laboratory at Orlando, Fla., the lice were kept thriving on their favorite food. Hired human hosts lay face down on cots, their backs covered with lice (one young woman was able to put herself through college as this kind of hostess). Dr. E. F. Knipling finally did these people out of a job by breeding lice which could live on special rabbits.

Then he fed all sorts of insecticides to the rabbits. Some killed the lice, but also killed the lousy rabbits. At last he found a compound (2-pivalyl-I, 3-indandione) which had no apparent effect on the rabbit, but killed all lice that took a single nip. Dose required: 2.5 milligrams (.00006 oz.) per kilogram (2.2 lbs.) of rabbit weight. One-tenth of a milligram fed daily for three weeks was deadly to lice for a month after the dosing stopped. A similar campaign against mosquitoes was not quite so effective. At Kerrville, Tex., an offensive against cattle ticks and lice is still in the early stages.

The Department's scientists consider their results inconclusive, but definitely promising. They have a lot more chemicals to try, and they have already established that slight changes in a compound's molecular structure sometimes make it more poisonous to insects or less poisonous to higher animals. Eventually they hope to find a Jekyll-Hyde chemical that will flow harmlessly in the veins of humans, but knock off any insect that sucks the human's blood.

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