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218 CHAPTER 13 1948 Guide measures, (o) suppression of dust and lint, and (5) disinfection of dropletnuclei. Well controlled, large scale tests of the various methods of air sterili zation conducted in barracks 1 4 have confirmed the importance of dust control in minimizing the spread of airborne disease, a consideration which has guided the practices of ventilating engineers for a number of years. The importance of the dust factor has been emphasized by many engineers and. has been convincingly demonstrated by subsequent bacteriologic studies aboard ships. Treatment of floors and bedclothes with oil emulsions has proved effective in reducing bacterial dispersion by as much as 90 per cent in Army barracks and station hospitals 4.. The incidence of acute respiratory Air Conditioning in the Prevention and Treatment of Disease __________________ 219 sively at the Naval Training Center, Sampson, N. Y. In barracks housing . naval recruits, hospital admissions for respiratory infections (mostly i catarrhal fever) were 25 per cent lower in a group of men exposed to ultra violet radiation--(2537 Angstrom Units, 1 to 7 ergs per (cm-2) (sec) at bed level)--than they were in adjacent control barracks without ultra' violet radiation 8. A combination of ultraviolet radiation and dust control measures is believed to be more effective than when either one of the two is used alone, but the proof for this has yet to come. The present status (1947) is admirably reviewed by the Committee on Sanitary Engineering of the National Research Council 9, and by a subcommittee of the American Public Health Association I0. Both com- mittees feel that the problem of air disinfection is still in the experimental stage, and that-present evidence does not warrant the use of ultraviolet radiation or glycol vapors in public buildings and industries in the hope of reducing respiratory infections. Much more experimentation is needed for arriving at a definite conclusion. Occurrence of diseases causing disability for 8 consecutive days or longer in a group of i00,000 wage earners (10 per cent women) in different industries. "Graph obtained from Dean K. Brundage, U. S. Public Health Service. Fig. 1. Study of Average Monthly Frequency (1921-1926 inclusive) of Specified Respiratory Diseases infections was from 10 to 30 per cent lower, in barracks with oiled floors and bedclothes than it was in control barracks which received no special treatment. More recent studies, however, have yielded inconsistent results. No simple method for disinfecting droplet-nuclei has yet been devised. Under favorable laboratory conditions, propylene glycol in concentrations of 0.07 to 0.14 milligrams per liter, and triethylene glycol in a concen tration of 0.0045 milligrams per liter were highly germicidal for 'most airborne bacteria in clean air when the relative humidity was between 40 and 60 pier cent516-7. Under practical conditions, however, particularly in the presence of dust in the air, glycol effectiveness is much reduced. The use of other chemical aerosols that have been tried is iimited by their toxicity, odor, or destructiveness to fabrics and metals. Ultraviolet radiation of floors and upper air has been studied exten- VALUE OF AIR COOLING UNDER TROPICAL CONDITIONS The commissioning of a class of naval hospital ships with all wards, laboratories and living spaces air cooled is a notable achievement to provide better treatment of patients, especially those suffering from extensive burns, by control of environmental factors. Although statistics are not at hand to indicate the deaths or retarded recoveries of patients due to lack of air cooling in ships operating in tropical waters, it is generally agreed among competent observers that high temperature and humidity are major factors in prolonging disability and increasing mortality of the sick and injured. Physiologic data obtained on healthy men, moreover, show the large loss of body fluids and the stress on the cardiovascular system in terms of increased pulse rate when these men are continuously subjected to high temperatures. Even at rest about 50 cc of fluid per hour are lost as sweat11 through intact skin. In burn patients the difficulty, encountered in temperate climates, of maintaining fluid and electrolyte balance is tremendously augmented by the addi tional evaporative fluid loss in hot environments;