Medicine: Protective Placenta

Few babies under six months catch measles, scarlet fever, diphtheria or infantile paralysis. Why, asked Drs. Charles Fremont McKhann Jr. & F. T. Chu of Harvard's pediatrics department.

Other investigators think the infants get their immunity from their mother's blood or milk. But there are arguments against that conception. A more tenable theory: the rapidly multiplying fetal and infant cells may establish a general protection called ''tissue immunity." If so, opined Drs. McKhann & Chu, the placenta (afterbirth) must contain substances which would prevent measles, scarlet fever, diphtheria and infantile paralysis in older children. With this idea they made some water extracts of after-births.

First they proved on guinea pigs, rabbits and themselves that the placental extracts were not poisonous and caused no sex derangements. Then on guinea pigs, rabbits and monkeys they demonstrated that the extract neutralized diphtheria toxin and infantile paralysis virus, and caused scarlet fever rashes to blanch. By good fortune 15 children who never had had measles were exposed to measles in Drs. McKhann & Chu's hospital. Ordinarily every one of them would have caught it. So the doctors took a small risk by injecting each child with the placental extract. Fourteen children showed no signs of measles. The fifteenth had a mild attack.

Last week the Journal of the American Medical Association took note of Drs. McKhann & Chu's work and applauded: ''Certainly ... a new approach to the prophylaxis and treatment of infectious diseases."