Medicine: Air Germicide

A powerful preventive against pneumonia, influenza and other respiratory diseases may be promised by a brilliant series of experiments conducted during the last three years at the University of Chicago’s Billings Hospital. Dr. Oswald Hope Robertson last week was making final tests with a new germicidal vapor—propylene glycol—to sterilize air. If the results so far obtained are confirmed, one of the age-old searches of man will finally achieve its goal.

The idea of sterilizing the air is not new —London’s great fire of 1666, for example, was touched off by the countless fires which townsmen lit to purge the air of plague. Use of chemical sprays to control air contamination was first attempted in 1928 by three doctors who tried a fine mist of sea water containing sodium hypochlorite. This venture gave promising results, but all such research lapsed for another decade. Within the last few years, several research groups (notably the University of Pennsylvania’s new Air-Borne Disease Laboratories) again began testing various sprays. Many chemicals were found to kill airborne micro-organisms quickly, even in concentrations as low as one gram of chemical per 500 cu. ft. of air. Trouble was that all these air germicides smelled bad, or were toxic, or irritated the respiratory tract. Dr. Robertson’s propylene glycol vapor is odorless, tasteless, nontoxic, non-irritating, cheap, highly bactericidal.

Its discovery was accidental. Dr. Robertson and his colleagues were trying out another possible germicide—a detergent or “soapless soap” (similar to Dreft, Aerosol and other products widely sold for household and industrial use). Water solutions of the detergent were only mildly effective, so the researchers tried solutions of detergents in propylene glycol, which is a sort of thin glycerine. Results were much better. Then the researchers found that the propylene glycol itself was a potent germicide. One part of glycol in 2,000,000 parts of air would—within a few seconds—kill concentrations of air-suspended pneumococci, streptococci and other bacteria numbering millions to the cubic foot.

How did it work? Respiratory disease bacteria float about in tiny droplets of water breathed, sneezed and coughed from human beings. The germicidal glycol also floats in infinitesimally small particles. Calculations showed that if droplet had to hit droplet, it would take two to 200 hours for sterilization of sprayed air to take place. Since sterilization took place in seconds, Dr. Robertson concluded that the glycol droplets must give off gas molecules which dissolve in the water droplets and kill the germs within them.

Dr. Robertson placed groups of mice in a chamber and sprayed its air first with propylene glycol, then with influenza virus. All the mice lived. Then he sprayed the chamber with virus alone. All the mice died.

Propylene glycol is harmless to man when swallowed or injected into the veins. It is also harmless to mice who have breathed it for long periods. But medical science is cautious—there was still a remote chance that glycol might accumulate harmfully in the erect human lungs which, unlike those of mice, do not drain themselves. So last June Dr. Robertson began studying the effect of glycol vapor on monkeys imported from the University of Puerto Rico’s School of Tropical Medicine. So far, after many months’ exposure to the vapor, the monkeys are happy and fatter than ever. Dr. Robertson does not expect mankind to live, like his monkeys, continuously in an atmosphere of glycol vapor; but it should be most valuable in such crowded places as schools and theaters, where most respiratory diseases are picked up.