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EFFECT OF AIR IONS ON BACTERIAL AEROSOLS
Philips (US Army Bacteriol. Labor.),Harris and Jones -1964 International Journal of Biometeorology. Vol.8 , Number 1, pp 27-37
One of most important international work concerning the interactions between electric charge and aerosol . It relates to a fluorescein salt aerosol [ 1 ], and an aerosol of Serratia Marcescens [ 2 ], banal but dreaded bacterium in hospital medium (responsible for serious pathologies of opportunity).
During many repeated experiments, the authors always observe: - that ionization does not disturb the size of the aerosols, whose decrease respects in all the cases the usual exponential law, and that the high speed of decrease of the aerosol [ 1 ] is identical with a positive or negative charge (speed = 5 times witness) - that the high speed of decrease of the aerosol [ 2 ], always higher than that of the aerosol [ 1 ], is increased 54% minimum with a positive load, of 78% minimum with a negative charge (Cf. Fig.) . - that the preliminary negative ionization of the room of experiment strongly increase the speed of decrease of the aerosol [ 2 ], indicating a fundamental difference in action of the positive and negative charges on the aerosol [ 2 ] - that the positive ions do not cause the death of the germs, whose decrease is only " physical " - that contrary, the negative ions involve always simultaneously a "physical " decrease much faster (precipitation), and the death of a large fraction of the germs (growing with time) .
CONCLUSION OF THE AUTHORS
"The amplitude of the exponential decay of the aerosol under the described conditions, makes ionization a parameter of quality. Although the effect of decrease observed is always due to the ions and of a " physical " nature, one observe with the negative ions only obviousness repeated of died of a large quantity of germs of the aerosol". 27 Int. J. Biometeor. 1964, vol. 8, number 1, pp. 27‑37
Effect of Air Ions on Bacterial Aerosols by G. Phillips*, G. J. Harris and M. W. Jones
INTRODUCTION
Current interest in research on air‑borne infection and in the technology for exerimental aerobiology as illustrated by the recent Conference on Air‑Borne Infection McDermott, 1961)‑ emphasizes the importance of control of environmental variables during laboratory studies with microbial aerosols. The environmental factors generally considered as requiring measurement and control in quantitative biological aerosol research are temperature and humidity. To a lesser extent, the effects of light and air pollutants have been considered. The present research constitutes a preliminary effort to evaluate the possible influence of gaseous air ions during experimental studies with microbial aerosols. Air ions have been defined as electrically charged submicroscopic particles of gaseous or solid matter (Kornblueh, 1958). Positive ions are created by the removal of an electron from an atom or molecule; negative ions are formed by the addition of an electron. Krueger, Smith and Go (1957) speak of small air ions as consisting of single ionized molecules about which cluster from 4 to 12 uncharged molecules''. Since it was first demonstrated in 1899 that charged air particles are responsible for the electrical conductivity of the atmosphere (Wilson, 1899), investigators in a number of disciplines have conducted studies on the influence of air ions on living matter. Claims made by many early investigators, who were hampered by the lack of proper means for generating and measuring air ions, gave rise to much controversy, some of which exists to the present time. During the past decade a considerable increase in air ion research was made possible by the development of adequate instrumentation. From the accumulated weight of these studies there can be little doubt that air ions, when applied in controlled experiments, are responsible for certain reproducible biological and physical changes, although it is generally believed that these changes are of a low order of magnitude (Krueger, 1962 . The most convincing evidence of the biological effects of air ions is that developed by Krueger and Smith, 1957; 1958a, b; Krueger, Smith and Miller, 1959; Krueger et al., 1959. These studies have shown that air ions have a significant and reproducible effect on the ciliary beat rate, the mucous flow rate, and the reaction to trauma of the trachea of laboratory animals. Moreover, these investigators have shown that negatively charged oxygen molecules and positively charged carbon dioxide molecules are probably the mediators of air ion effects (Krueger and Smith, 1959). Recent work by this group (Krueger, 1962) indicates that effects in the trachea depend upon the ability of positively charged carbon dioxide ions to cause a local accumulation of 5‑HT in the tissue, and the ability of negatively charged oxygen ions, acting on cytochrome oxidase, to accelerate the oxidation of free 5‑HT. Krueger's studies have obvious relations to problems of experimental respiratory infections that are not treated in this paper. Other recent research on air ions has represented broad interests. Kornblueh et al. (1958) have evaluated negative air ion therapy for patients with hay fever, bronchial asthma, and certain respiratory difficulties and have used negative ion therapy as
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an adjunct in the treatment of burned patients (David, Minehart and Kornblueh, 1960). Other recent studios on the biological effects of ai‑r ions have included effects on the rate of growth of tissue culture cells (Worden and Thompson, 1956; Worden, 1961), blood pH, carbon dioxide combining power of animal plasma (Worden, 1954), and human work performance and visual reaction time (Slote, 1962) In most studies the magnitude of the reported changes or effects was not large, although there was rather general agreement that positive ions are associated with harmful or undesirable effects and negative ions stimulate or are associated with beneficial effects. 0ther research has been concerned with the physics of air ions and their interactions with non‑biological air constituents. These have added much to our present knowledge of expected ambient air ion densities (Davis and Speicher, 1962), the effects of air ions on inert aerosols (Whitby and McFarland, 1961), and the effects of aerosols on air ions (Ruhnke, 1962). Although a number of authors have reported that air ions affect microorganisms, the only quantitative study to date is that of Krueger, Smith, and Go (19571. These investigators measured the survival of MICROCOCCUS PYOGENES var. AUREUS in droplets placed in porcelain microtitration dishes and exposed to air ions at concentrations of 1 x 10 ions/cm3/sec, or greater. In the absence of smog, exposure to positive or negative ions increased the death rate of the staphylococci in the droplets, apparently by direct action on the bacteria and by increasing the droplet evaporation rate. In the presence of smog, air ions exerted a protective effect on the bacteria by reducing the droplet evaporation rate and delaying the drop in pH. The experiments also indicated that the action of the air ions on the cells could be partly reversed by exposure to intense visible light.
METHODS AND MATERIALS
A. EXPERIMENT DESIGN Aerosols of SERRATIA MARCESCENS an 4 di‑sodium. fluorescein singly and in combination were generated in a 365‑liter chamber containing a generator capable of producing negative or positive air ions. The aerosol density was measured at designated intervals during the life of the cloud. Each test consisted of 3 treatments: negative ions, positive ions, and no added ions.The order of the treatments was randomized through‑out all tests and a sufficient number of replicate tests were performed to establish statistical validity. The objectives of the experiments were: (a)To measure the rate of decay of aerosols in the presence of artificially produced positive and negative air ions as compared with the rate of decay obtained when no ions were added. (b)To determine whether the following factors affect these rates: (1)Residual effects emanating from the ion‑generating equipment(control test). Time (2)at which air ions are added to the test‑atmosphere. (3) Particle size spectrum of the bacterial aerosols. (4) Physical versus biological characteristics of aerosol decay.
B. AIR ION GENERATING AND MEASURING EQUIPMENT A Philco Model RG‑4 generator *) capable of producing air ions of either polarity and equipped with a small fan was used throughout. The ionizer unit was placed inside the aerosol chamber with its controls and power supply unit on the outside. The maximum output setting was used for all tests. Using the Philco Model ICF‑6 ion counter, the approximate maximum air ion concentration in the chamber (without aerosol) was 900 000 /cm3 of air. During all tests the generator fan was used to maintain homogeneity in the aerosol. C. PRODUCTION AND SAMPLING OF AEROSOLS The bacterial aerosol generator was a simple two‑fluid spray tube capable of dis seminating a total of one ml of liquid material. Aqueous solutions of 0.1% di‑sodium * Philco Corp., Communication and Weapons Division, 4700 Wissihickon Ave., Philadelphia 44, Pa. 29
fluorescein or broth suspension containing approximately 10 x 109 viable cells of SERRATIA MARCESCENS were used to charge the aerosol generator. In some tests a mixture of fluorescein and bacterial cells was used. After aerosol generation (requiring about 3 sec), samples of the aerosol were taken at 4,8 , and 12 min to determine the amount of fluorescein and the numbers of viable organisms air‑borne per unit volume of air. Sampling was done with all‑glass impingers *) (AG1) containing 20 ml of sterile physiological saline and operated at a sampling rate of 12.5 L/min for 1 min. The collecting fluid containing the entrapped microorganisms was assayed for viable cell concentration by preparing serial dilutions and plating samples in quaduplicate on the surface of agar plates. The selective nutrient agar used was Difco Peptone Agar**) to which was added 0.001% Actidione***) to inhibit fungal contaminants and 250 mg/l of brilliant green dye to inhibit Gram‑positive microorganisms. Fluorescein collected in the sampler fluid was assayed photofluorometrically by comparison with standard solutions and the results expressed in fluorescein mg/ml. Following each test, the microorganisms remaining air‑borne were reduced to an insignificant order of magnitude by irradiating the interior of the chamber with a 15 watt ultraviolet lamp****) for 5 min with the mixing fan operating.
D. METHOD OF ANALYSIS Considerable variation occurred in the concentration of air‑borne SERRATIA MARCESCENS cells obtained during the first sampling period of the various replications. However, since we were primarily interested in comparing decrease of concentration with time, rather than per cent recovery, the statistical analysis was confined to decay rates. From theoretical considerations, it was expected that the change in aerosol concentration with time would be proportional to concentration, i.e. where C = aerosol concentration, t = time, and k = proportionality constant. This gives rise to the model where C = initial concentration of aerosol. This was found to describe the data extremely well. The exponential decay rate is defined as 100 k, expressed as per cent per minute, where k is taken from the model above. Taking natural logarithms of Equation (2), we have the linear form In this form k is readily recognized as the slope of the linear regression of the logarithm of concentration versus time. Over the range of concentrations of air‑borne material observed in this study, the decay parameter was independent of initial concentration, thereby permitting valid treatment comparisons to be made on the basis of the exponential decay rates alone. Student's ''t'' test was used for treatment comparisons .
RESULTS RESIDUAL EFFECTS OF ION GENERATING EQUIPMENT (Control Tests)
Since the ion generator with its fan and electrical lead wires remained in the aerosol chamber during all tests, it was necessary to determine if the instrument itself and its energized circuitry affected the decay of aerosols. Tests were done, *)All‑Glass Impinger Sampler, Ace Glass Co, Vineland, N.J. **)Difco Company, Detroit, Michigan. ***)Upjohn Pharmaceutical Co., Kalamazoo,Michigan. ****)Ultraviolet Lamp, HC‑15, Westinghouse Electric Corp., Bloomfield, N.J. 30 therefore, under simulated positive, simulated negative, and control conditions with the corona tip of the generating probe covered with a plastic envelope to preclude dissemination of air ions. The power supply and polarity switches were operated in the usual manner so that all circuits were energized up to the probe tip as they would be in the usual experiment. We used the Philco Ion Collector to determine that no air ions were released through the plastic envelope into the aerosol chamber. Data obtained from 6 trials, each with random‑order treatments, are shown in Table L. No significant differences in exponential decay rates were obtained; therefore, t was concluded that the instrument itself and the energized circuits (not including the probe) would not affect the decay of aerosols in subsequent experiments.
TABLE 1.Analysis of exponential decay rates of S. MARCESCENS aerosols as affected by residual effects from the ion generator
Exponential decay rates, per cent minute
Number 95% of MeanSE confidence Treatment tests limits
No added ions 6 20.6 5,84 1.45 ‑ 26.8 Negative ion circuit 6 24.6 7.81 16.4 ‑ 32. Positive ion circuitry 6 21.1 8.18 12.5 ‑ 29.6 Treatment Comparisons Computed Approx. "t" Probability No added ions vs. negative circuitry 1.01 NS* No added ions vs. positive circuitry < I NS Negative circuitry vs. positive circuitry < I NS *) No significant difference.
DECAY OF FLUORESCEIN AEROSOLS Although the removal of inert aerosols by interaction with air ions has been re�ported, it was of interest to test the effects in these investigations, using the generation and sampling equipment described. In 5 replicate tests, with random‑order treatments, air ion generation was started 5 min before aerosolization of a 0.1% so� lution of di‑sodium fluorescein. After operation of the aerosol generator, samples of the fluorescein content of the air were obtained at 4, 8, and 12 min. Under the control conditions (no added air ions) the exponential decay rates for di‑sodium fluorescein were considerably less than those for S. MARCESCENS aerosols. This was expected because of the biological nature of the latter. The presence of positive or negative air ions in the chamber caused a fivefold increase in the exponential decay rates of fluorescein aerosols that was significant at less than the 0.01 level. There were no significant differences in exponential decay rates between the two ion polarities. The decay rates obtained and their analysis are shown in Table 2.
DECAY OF SERRATIA MARCESCENS AEROSOLS The effects of air ions on the total decay of air‑borne bacterial cells were estimated by analysis of data obtained from 18 replicate trials, each with 3 air ion treatments arranged in random sequence. In these tests, as in the fluorescein tests, generation of air ions was begun 5 min before creation of the S. MARCESCENS aerosol. Although from day to day there was considerable variation in the initial concentration of aerosol produced, probably because of temperature, relative humidity, and other variations that could not be controlled in the aerosol chamber, conduct of all 3 treatments during each day provided a basis for comparing the data obtained. Several trials were discarded in which the results of one of the 3 treatments on one day were lost because of malfunction of equipment. 31
TABLE 2. Analysis of exponential decay rates of fluorescein aerosols in the presence and absence of air ions
Exponential decay rates, per cent per minute Number 95% Treatment of Means SE Confidence tests limits
No added air ions 5 6.3 1.12 4.9 ‑ 7.7 Negative ions 5 33.1 5.98 25.7 ‑ 40.5 Positiveions 5 31.9 6.05 24.4 ‑ 39.4
Treatment Comparisons Computed ''t'' Approx. Probability
No added ions vs. negative ions 9.83 <0.01 No added ions vs. positive ions 9.32 <0.01 Negative ions vs. positive ions <1 NS
It was evident from the results that the decay of S. MARCESCENS aerosols was more rapid in the presence of artificially generated air ions of either polarity than in their absence. Table 3 shows the mean viable cell concentration in the aerosol at the 4‑, 8‑, and 12‑min sampling times for the 3 treatments. Conversion of the aerosol concentrations from individual tests to exponential decay rates and analysis of the means of the rates, as in previous tests, showed the exponential decays in ionized air to be from 2 to 3 times that of the control. TABLE 3. Mean aerosol recovery of S. MARCESCENS in the presence and absence of air ions*
S. MARCESCENS cells per liter of air Treatment Age of aerosol 4 minutes 8 minutes 12 minutes No added ions269,333 122,227 42,597 Negative ions 63,114 5,363 ?557 Postitive ions 70,013 7,707 1,238
*Mean of 8 tests
This analysis, shown in Table 4, shows that not only were the exponential decay rates in both test atmospheres significantly higher than the control decay rates, but that the negatively charged atmospheres resulted in higher exponential decay rates than positively charged atmospheres. A graphical comparison of the decay of S. MARCESCENS aerosol with time for the 3 treatments is shown in Fig. 1. In this illustration the derived k values were used, taking the initial recovery as 100 per cent.
INFLUENCE OF TIME OF ADDITION OF AIR IONS In the previous tests the ionizer was turned on 5 min prior to aerosol generation. It was determined that during this period an equilibrium concentration of air ions (approximately 900 000/cm3of air) was established. Further, it was postulated that if such an initially high ion level were necessary to obtain the observed results, allowing the aerosol to come to equilibrium before introducing air ion 8 might improve the survival of aerosolized bacteria. 32 TABLE 4.Analysis of exponential decay rates of S.MARCESCENS aerosols in the presence and absence of air ions
Exponential decay rates, per cent per minute
Number 95% of MeanSE Confidence tests limits Treatment No added ions 18 22.7 7.03 19.2 26.2 Negative ions 18 78.1 31‑71 62.3 93.8 Positive ions 18 53.6 6.11 50.6 56.7
Treatment Comparison Computed ''t'' Approx.Probability No added ions vs. negative ions 7.22 < 0.01 No added ions vs. positive ions 14.10 < 0.01 Negative ions vs. positive ions 3.21 < 0.01
The influence of time was tested in a series‑of 8 tests in which the ionizerwas not turned on until immediately after the 4‑min sample was taken. A series of 10 tests from those in Table 4, which were done in the previous 2 weeks and in which the ionizer was turned on prior to aerosolization, was used for comparison. Mean exponential decay rates for the 2 series of tests are shown in Table 5. In each series, negative and positive ion treatments produced exponential decay rates higher than the controls, but we failed to demonstrate significant differences between rates in negative as compared with positive ion atmospheres. Comparison of means from the two series, also shown in Table 5, indicated that, for both controls and positive ion atmospheres, the influence of time of addition of air ions was negligible. For negative ion atmospheres, however, addition of air ions before aerosolization resulted in a higher exponential decay rate than when air ions were added after aerosolization. Thus it appears that time of addition of the ions is important for negative ions but of little importance for positive ions. 33
TABLE 5. Exponential decay rates of S. MARCESCENS as influenced by time of addition of air ions Ions added before Ions added after Comparison of aerosolization aerosolization means for time (10 estimates)(8 estimates) air ions added Treatment Mean exp. Mean exp. decay rate, decay rate, Computed Approx. %/min SE %/min SE "t" Probability No air ions 24.5 7.30 20.4 4.37 1.47NS Negative ions 75.6 29‑51 50,6 9.50 2.52<O‑05 Positive ions 55.4 5.81 55.7 21.69 1 NS
Computed Approx. Computed Approx. Comparisons Probability "t" Probability No air ions vs. negative ions 5.32 <0.01 8.80 <0.01 No air ions vs. positive ions 10‑50 <0.01 4.51 <0.01 Negative vs. positive ions 2.12 NS <1 NS
DECAY IN RELATION TO AEROSOL PARTICLE SIZE The aerosol generator used produces particles that are initially smaller than five microns in diameter. The AGI sampler is selective for aerosol particles of approximately 17 /A and smaller. The addition of a pre-impinger to the AGI provides a sampler that is selective for particles of 5 Ix and smaller. Thus, operation of the AGI simultaneously with the AGI plus pre‑impinger provides a convenient method of partitioning aerosols into 2 size ranges. This technique was used in further experiments to determine if the size of the viable particles in the air changed with time during the ionization treatments compared with those in the control. It was hypothesized that if, during ionization, the size of the air‑borne particles tended to increase with time compared with the control, increased agglomeration by air ions would result in increased settling and be one mechanism responsible for the increased decay rates. In 4 tests of 3 treatments each we sampled the aerosol simultaneously with the AGI and with the AGI plus pre‑ impinge r. The aerosol concentrations from the duplicate samples at each sampling period were) not significantly different. Exponential decay rates were also compared (Table 6 There were no significant differences in the rates when the two sampler results for each treatment were compared. It was concluded, therefore, that within the accuracy of the sampling devices, the air‑ion‑treated aerosols did not differ in particle size range from the aerosols in the control environment for as much as 12 min of aerosol life. PHYSICAL VERSUS BIOLOGICAL DECAY From a comparison of the exponential aerosol decay rates of fluorescein (Table 2) and S. MARCESCENS (Table 4), it is obvious that the decay function of the latter can be composed of a biological component (death of the cell) and a physical component (evanescence). The final tests were performed by aerosolizing a mixture of fluorescein solution and S. MARCESCENS culture to allow simultaneous assessment of both ingredients. The purpose of the tests was to obtain an estimate of the proportions of the total decay of S. MARCESCENS due to physical fallout and to biological death. In 4 replicate tests, the order of the 3 treatments was randomized and the generation of air ions was begun 5 min before aerosolization. The fluid from each sampler was analyzed first for number of viable cells of S. MARCESCENS and then for fluorescein content. Reduction of viable air‑borne S. MARCESCENS as a function of time was taken as an estimate of total decay, the reduction in fluorescein as physical decay, with the difference between the 2 representing an estimate of biological decay. 34 TABLE 6.Comparison of exponential decay rates of S. MARCESCENS in air ion atmospheres in relation to particle diameter
Mean exponential decay rates, per cent per minute Treatment AGI sampler, AGI + pre‑impinger sampler
No added air ions 17.2 21.6 Negative ions 89.2 64.5 Positive ions 52.3 59.2
AGI vs. AGI + pre‑impinger Treatment Computed ''t'' Approx.Probability
The results are shown in Tables 7 and 8. In the control tests (no added ions) about three‑quarters of the total decay was due to biological death, biological decay being significantly higher than physical decay. The total decays and the physical decays under the influence of air ions were significantly higher than in the controls. In comparing biological decays, however, no significant increase over the control by positive ion treatment (17.6 vs. 27.8%/min) was noted, although negative ion treatment produced a significantly higher biological decay than the control. But when the combined effects of physical and biological decays in the presence of each ion charge were compared, no significant difference was noted.
TABLE 7. Estimates of biological and physical aerosol decays in the absence and presence of air ions Exponential decay rates, per cent per minute Total Treatment Physical decay Biological decaydecay No added ions 6.4 17.6 24.0 Negative ions 27.4 45.7 73.1 Positive ions 22.7 27.8 50.5
TABLE 8. Analysis of differences between estimates of biological, physical, and total aerosol decay rates in the absence and presence of air ions
Biological decay Physical decay Total decay Treatment comparison "t"Prob‑"t" Prob‑ "t" Prob‑ ability ability ability No added ions vs. negative ions 3.24 <0.05 2.80 <0.05 3.41 <0‑05 No added ions vs. positive ions 1.65 NS 3.39 <0.05 4.60 <0.05 Negative ions vs. positive ions 1.92 NS < 1 NS 1.55 NS
Treatment Physical vs. Biological decay Computed ''t'' Approx. Probability No added ions 3.04 0.05 Negative ions 1.6s NS Positive Ions < 1 NS
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These tests show that the major part of the decay of S. MARCESCENS aerosols in the absence of air ions is due to biological decay; in the presence of air ions, a greater relative amount of physical decay occurs. Moreover, there appears to be a selective difference in the biological decay resulting from positive and negative ion exposure, with negative ions having a greater biological effect than positive ions.
CONCLUSIONS
The most important conclusion drawn from these studies is that artificially produced air ions will increase to a significant extent the exponential decay rates of aerosols of S. MARCESCENS and di‑sodium fluorescein. Exponential decay values, defined as 100 k and expressed as %/min, were increased 2‑ to 5‑fold by air ions. Analysis of the 34 aerosol trials, each with positive ion, negative ion, and control treatments, resulted in the following findings: (1) Aerosols of di‑sodium fluorescein in the presence of negative or positive air ions decayed at a rate approximately 5 times that obtained under control conditions. There was no selective difference between the action of negative and positive ions. (2) SERRATIA MARCESCENS aerosols not in the presence of added air ions showed exponential decay rates approximately 4 times greater than fluorescein aerosols without air ions. Under the influence of air ions the exponential decay rates for S. MARCESCENS were increased from approximately 23%/min for the control to 54%/ min for positive ions and 78%/min for negative ions. The action of negative ions was significantly greater than that of positive ions. (3)When the procedure of adding aerosol to an atmosphere already containing air ions was compared with the addition of ions after aerosol generation, there was no difference in decay rates with positive ions. However, with negative ions, ionization of the chamber before aerosol generation resulted in significantly higher exponential decay rates.. This suggests that a basic difference exists in the mechanism of action of positive and negative air ions on microbial aerosols (4)No significant differences were detected in the size of the air‑borne particles that were predominantly less than five microns in diameter at the 4‑, 8‑, and 12‑min. sampling intervals. Ionization did not change the general size? range of the particles in the air during these intervals. The relative diameter of the fallout particles during the various treatments was not assessed.‑ (5) Most of the increase in total decay brought about by air ions was reflected in the physical decay component. Positive ion treatment did not increase exponential biological decay as compared with control tests. However, in addition to the increase in physical decay, negative ions produced a significant increase in biological decay. These experiments show that decay of aerosols as a function of interaction with air ions can be delineated in a simple aerosol test facility. The magnitude of the increased exponential decay under the conditions specified in these tests was sufficient to characterize air ions as a parameter possibly deserving control. Although most of the observed increase in decay can be said to be due to the physical action of air ions, there was repeated evidence that negatively charged ions, in contrast to positively charged ions, are responsible for a significant amount of biological aerosol death.
36 REFERENCES
DAVIS, F.K., Jr. and SPEICHER, R.P. (1962): ''Natural ion levels in the city Of Philadelphia". Proc. IRt. Conf. OR Ionization of the Air. Am. IRst. Med. Climatology, Philadelphia, I : 1‑16 (XI). DAVID, T.A., MINEHART, J.R. and KORNBLUEH, I.H. (1960):''Polarized air as an adjunct in the treatment of burns''. Am. J. phys. Med., 39 : 111‑113. KORNBLUEH, I.H. (1958) ''Brief review of effects of artificial ionization of the air and ultraviolet radiation''. Int. J. Bioclim. Biometer., 2 : part 4, Section Coe. * KORNBLUEH, I.H., PIERSOL, G.M. and SPEICHER, F.P.: ''Relief from pollinosis in negatively ionized rooms''. Arn. J. phys. Med., 37 : 18‑27. KRUEGER,.A.P. (1962)''Air ions and physiological function''. J. gen. Physiol., 45 : 233‑241. KRUEGER, A.P. and SMITH, R.F. (1957): Affect of air ions on isolated rabbit trachea". J. exp. Biol. Med., 96 : 807‑809. KRUEGER, A.P. and SMITH, R.F. (1958a): "Effect of gaseous ions on tracheal ciliary rate''. J. exp. Biol. Med., 98 : 412‑414. KRUEGER, A.P. and SMITH, R.F. (1958b): ''The effect of air ions on the living mammalian trachea'' J. gen. Physiol., 42 : 69‑82. KRUEGER, A.P. and SMITH, R.F. (1959: ''Parameters of gaseous ion effects on the mammalian trachea. A. Duration of effects. B. Minimal effective ion densities''. J. gen. Physiol., 42 : 959‑969. KRUEGER, A.P., SMITH, R.F.and GO, I.G. (1957): ''Action of air ions on bacteria''. J. gen. Physiol., 41 : 359‑381. KRUEGER, A.P., SMITH, R.F.and MILLER, J.W. (1959): ''Effects of air ions on trachea of primates''. Proc. Soc. exp. Biol. (N Y.), 101 : 506‑507. KRUEGER, A.P., SMITH, R.F., HILDEBRAND, G.J.. and MEYERS, C.E. 1959): ''Further studies of gaseous ion action on trachea''. Proc.Soc. exp. Biol. (N.Y.), 102 : 355‑357. McDERMOTT, W. (ed.) (1961): Conference on airborne infection''. Bact. Rev., 25:1‑377. RUHNKE, L.H. (1962) :''The change of the small ion density due to condensation nuclei and the relation to the extinction coefficient of light''. Proc.Int.Conf.on Ionization of the Air. Am. Inst. Med. Climatology, Philadelphia . SLOTE, L. (1962) : ''An experimental evaluation of man's reaction to an ionized air envoronment .� Proc. Int. Conf. on Ionization of the Air. Am. Inst. Med. Climatology, Philadelphia,II,1‑22(Xv). WHITBY, K.T. and McFARLAND, A.R. (1962): ''The decay of unipolar small ions and homogeneous aerosols in closed spaces and flow systems''. Proc.Int.Conf. on Ionization of the Air.Am.Inst.Med.Climatology,,� WILSON, C.T.R. (1899) ''On the comparative efficiency as condensation nuclei of positively and negatively charged ions''. Phil. Trans.A., 193 : 289‑308. WORDEN, J.L. (1954) effects of air ion concentration and polarity onthe carbon dioxide capacity of mammalian blood plasma''. Fed. Proc., 13 : 557. WORDEN, J.L. (1961) ''Proliferation of mammalian cells in ion‑controlled envi� ronments''. J.Nat.Cancer Inst., 26 : 801‑811. WORDEN, J.L. and THOMPSON, J.R. (1956): ''Air ion concentration and the growth of cells in vitro''. Anat. Record, 124 : 500.
ABSTRACT
The effect of positively and negatively charged air ions on aerosols of SERRATIA MARCESCENS was evaluated by comparing rates of exponential bacterial decay. Ions of both polarities were responsible for significant increases in the mean exponential decay rates when compared with a non‑ionized ambient atmosphere. Negative ion atmospheres were shown to be slightly more active than positive ion atmospheres, which is probably‑due to a greater biological action of negative ions. 37
ZUSAMMENFASSUNG
Die Wirkung von positiven und negativen Luftionen auf SERRATIA MARCESCENS Aerosole wurde untersucht. Im Vergleich zu nicht ionisierter Luft f�hrte Luft mit positiven und negativen Ionen zu einem signifikanten Anstieg der exponentiellen Absterbrate. Negativ ionisierte Luft war etwas wirksamer als positiv ionisierte Luft. Dies ist wahrscheinlich Ausdruck der st�rkeren biologischen Wirkung der negativen Ionen.
RESUME
Les effets d'une ionisation positive ou n�gative de l'air ont �t� �tudi�s sur la vitesse de d�croissance d'activit� bact�rienne dans des a�rosols de SERRATIA MARCESCENS. Compar�es � des atmosph�res non ionis�es, les ions des deux polarit�s ont augment� cette vitesse, les ions n�gatifs s'av�rant largement plus actifs que les ions positifs, ce qui semblerait traduire une plus forte activit� biologique des ions n�gatifs.
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