INHIBITION OF PHOTOTAXIS IN Volvox aureus BY NATURAL AND SIMULATED SOLAR ULTRAVIOLET LIGHT

Exposure to artificial UV wavelengths and the UV component of sunlight delays positive phototaxis in the green alga Volvox aureus. Broad band wavelength filters were used to modify the output from UV-B sources (280-320 nm) and natural sunlight. The delay in phototaxis by artificial UV is increased with exposure to shorter UV-B wavelengths. Natural sunlight experiments were performed with exposure to full sunlight and to its UV component only. The UV component present in summer sunlight produced long periods of inhibition in phototaxis and even lethality, while exposure to the total spectrum of sunlight had no significant effects on movement or survival. The data indicate that although this species of alga is well equipped to deal with present levels of UV exposure, increases in the short UV-B wavelengths in sunlight may force an alteration in patterns of photomovement.     

INHIBITION OF PHOTOTAXIS IN Volvox aureus BY NATURAL AND SIMULATED SOLAR ULTRAVIOLET LIGHT

Abstract
Exposure to artificial UV wavelengths and the UV component of sunlight delays positive phototaxis in the green alga Volvox aureus. Broad band wavelength filters were used to modify the output from UV-B sources (280–320 nm) and natural sunlight. The delay in phototaxis by artificial UV is increased with exposure to shorter UV-B wavelengths. Natural sunlight experiments were performed with exposure to full sunlight and to its UV component only. The UV component present in summer sunlight produced long periods of inhibition in phototaxis and even lethality, while exposure to the total spectrum of sunlight had no significant effects on movement or survival. The data indicate that although this species of alga is well equipped to deal with present levels of UV exposure, increases in the short UV-B wavelengths in sunlight may force an alteration in patterns of photomovement.     

ENHANCED MACROPHAGE CYTOTOXICITY AGAINST TUMOR CELLS TREATED WITH PHOTODYNAMIC THERAPY

Abstract— Sulfamethoxazole (SMX) in its nonionized form in aqueous solution has ultraviolet (UV) absorption that is maximal at 268 nm but extends through the ultraviolet-B (UVB) region. It was found to be extremely susceptible to photodegradation when exposed to artificial UV radiation through a Pyrex filter or to unfiltered natural sunlight. The SMX anion was more stable. The quantum yields of the photodegradation of both forms were determined by use of monochromatic light and ferrioxalate chemical actinometry, the values of 0.47 (pH 3.0) and 0.084 (pH 9.0) at the maximum absorption wavelengths (268 and 257 nm, respectively) being obtained. Using literature data on sunlight intensity, the photochemical shelf-life of SMX solutions exposed to direct sunlight was calculated for Sydney (latitude 33.5°S) as a function of season of the year and verified experimentally. A fixed correlation was established between the rate constant for SMX degradation and UVB intensity measured by a radiometer, suggesting the capacity of this chemical system to monitor changes in the UVB region of sunlight.     

Exposure geometry and spectral environment determine photobiological effects on the human eye

Photobiological effects upon the human retina, cornea and lens are highly dependent on the optical exposure geometry as well as spectral characteristics of the exposure. The organ of sight is exquisitely sensitive to light because it performs well in very low nighttime illumination levels and yet it also must adapt to extremely bright environments where light exposures are greater by many orders of magnitude. The eye has evolved to protect itself reasonably well against excessive exposure in bright environments. The retina is minimally exposed in extremely bright environments and the cornea and lens are surprisingly well protected in harsh environments. Although these protective mechanisms are good, they are not perfect and adverse changes from both acute and chronic exposures to sunlight still exist. The geometrical protective factors must be understood and appreciated whenever assessing potential adverse effects of environmental UV radiation and light on ocular structures. These natural ocular protective factors also work with the ever-changing spectrum of sunlight and the different spectral distribution of light and UV radiation across the eye's field of view. Spectral characteristics of the ocular media are also important. One can visualize a series of intraocular color filters that progressively filter shorter wavelengths and thereby aid in color vision, reduce the impact of chromatic aberrations and significantly reduce the optical radiation hazards to the lens and retina.     

UV-induced changes in pigment content and light penetration in the fruticose lichen Cladonia arbuscula ssp. mitis

The response of the lichen, Cladonia arbuscula (Wallr.) Flot. ssp. mitis (Sandst.) Ruoss to enhanced UV-B (280-315 nm) radiation was investigated with respect to: (a) changes in phenolic content; (b) differential pigment accumulation under visible and UV radiation with increasing distance from thallus apices; and (c) the internal distribution of UV-B radiation within the thallus measured with quartz optical fibres. In a short-term experiment, lichens were exposed for 7 days in a growth chamber to visible light with or without additional UV-B radiation. For a longer term experiment, lichens were grown outdoors under both natural UV radiation, and supplemental UV-A (315-400 nm)+UV-B provided by lamps. Controls were placed under filters that removed the radiation below 290 nm from the natural sunlight. The concentration of total phenolic compounds was measured spectrophotometrically at the termination of the experiments, in different parts of the lichen podetia. UV-exposed lichens showed increased accumulation of phenolics compared to those not grown under UV. At the termination of the long-term experiment, fibre optic measurements of the penetration of radiation into lichen thallus reflected the influence of growth under UV radiation, whereby UV was more strongly attenuated as compared to that in lichens not exposed to enhanced levels of UV-B radiation. Results indicated that in Cladonia, UV-B radiation induces the accumulation of phenolic compounds that may have a protective role. In addition, the morphological distribution of phenolic compounds was different under visible and supplemental UV-B radiation. Internal radiation measurements served to visualise the attenuation of radiation with thallus depth for different wavelengths in the UV-B waveband.     

A SCALAR IRRADIANCE FIBER-OPTIC MICROPROBE FOR THE MEASUREMENT OF ULTRAVIOLET RADIATION AT HIGH SPATIAL RESOLUTION

Abstract— The construction of a new type of microprobe for the measurement of scalar irradiance (integral dose rate) in the UV down to wavelengths of 250 nm is described. The microprobes were made from tapered standard optical fibers and a tip-diffuser of magnesia/silica vitroceramic. The sensing tips were ca 100 μm in diameter and had maximal deviations in the angular response of ± 15%. I present measurements of scalar irradiance at high spatial resolution within dry beach sand and suspensions of microorganisms. These two media are environments in which microorganisms are exposed to UV, either under natural (sand) or laboratory conditions (suspensions). In both cases, the space distribution of UV scalar irradiance, and thus the distribution of integral dose rates, departed significantly from that predicted by absorptive effects alone. The results underscore the importance of small-scale, in situ measurements of scalar irradiance for UV dosimetry in such scattering media.     

Wavelength dependence of mycosporine-like amino acid synthesis in Gyrodinium dorsum

The synthesis or accumulation of mycosporine-like amino acids (MAAs) is an important UV tolerance mechanism in aquatic organisms. To investigate the wavelength dependence of MAA synthesis in the marine dinoflagellate Gyrodinium dorsum, the organism was exposed to polychromatic radiation (PAR and UV) from a solar simulator for up to 72 h. Different irradiance spectra were produced by inserting various cut-off filters between lamp and samples. A polychromatic action spectrum for the synthesis of MAA synthesis was constructed. PAR and long wavelength UV-A radiation showed almost no effect while the most effective wavelength range was around 310 nm. Shorter wavelengths where less effective in the induction of MAA synthesis. Wavelengths below 300 nm damaged the organisms severely as indicated by a decrease in chlorophyll a absorption.     

Inactivation of Virulent Burkholderia pseudomallei by Sunlight

The goal of this study was to determine the sensitivity of virulent Burkholderia pseudomallei to natural sunlight. We describe solar dosimetry calibrated to integrate radiation between 295 and 305 nm and an exposure system that minimizes thermal effects on bacterial cells. Burkholderia pseudomallei cells were either exposed to sunlight in UV transparent dishes or maintained in the dark covered by opaque foil. The cells maintained in the dark remained at constant levels for the duration of all experiments. The exposed cells nearby were killed with a kinetic studied through 5 Log₁₀ inactivation. We found that cells in stationary phase of growth were nearly two-fold more resistant to sunlight than cells in lag or exponential growth. A virulent strain of B. pseudomallei that produced mucoid colonies showed sensitivity to sunlight similar to both a virulent strain that produced nonmucoid colonies and a strain of B. thailandensis . The inactivation of B. pseudomallei by sunlight in different types of water of environmental relevance or inside amoebae was investigated. The sensitivity of virulent B. pseudomallei was calculated and its comparison with previous studies employing monochromatic germicidal light (254 nm) is discussed . This may be the first report in the open literature of the inactivation of a virulent biological threat agent by natural sunlight. These data should assist in estimating the risk for contracting melioidosis and in predicting the time period during which B. pseudomallei remains infectious after an accidental or intentional release in the environment.     

Daily and circadian variation in survival from ultraviolet radiation in Chlamydomonas reinhardtii

The survival of organisms depends on their ability to adapt to their environment, one important aspect of which is the daily cycle of day and night. During the day, organisms use a variety of strategies to protect themselves from deleterious ultraviolet (UV) wavelengths of sunlight. Among those strategies could be timing of UV-sensitive cellular processes to occur at night to avoid UV-induced damage. We tested whether the unicellular alga Chlamydomonas reinhardtii uses this strategy by measuring the survival of cells following exposure to UV radiation at different phases of the day. Chlamydomonas cells displayed a rhythm of survival from UV radiation where the most sensitive phases occurred during the end of the day and at the beginning of the night. This phase of sensitivity corresponds to the time of nuclear division. The rhythm continues in constant light indicating control by a circadian clock. The results presented here suggest a hypothesis of how circadian clocks may have evolved; a temporal program whereby light-sensitive processes are timed to avoid sunlight-induced damage would be advantageous and therefore selected.     

The role of solar UV radiation in the ecology of alpine lakes.

Solar ultraviolet radiation (UVR, 290-400 nm) is a crucial environmental factor in alpine lakes because of the natural increase of the UVR flux with elevation and the high water transparency of these ecosystems. The ecological importance of UVR, however, has only recently been recognized. This review, examines the general features of alpine lakes regarding UVR, summarizes what is known about the role of solar UVR in the ecology of alpine lakes, and identifies future research directions. Unlike the pattern observed in most lowland lakes, variability of UV attenuation in alpine lakes is poorly explained by differences in dissolved organic carbon (DOC) concentrations, and depends mainly on optical characteristics (absorption) of the chromophoric dissolved organic matter (CDOM). Within the water column of lakes with low DOC concentrations (0.2-0.4 mg l(-1)), UV attenuation is influenced by phytoplankton whose development at depth (i.e. the deep chlorophyll maximum) causes important changes in UV attenuation. Alpine aquatic organisms have developed a number of strategies to minimize UV damage. The widespread synthesis or bioaccumulation of different compounds that directly or indirectly absorb UV energy is one such strategy. Although most benthic and planktonic primary producers and crustacean zooplankton are well adapted to high intensities of solar radiation, heterotrophic protists, bacteria, and viruses seem to be particularly sensitive to UVR. Understanding the overall impact of UVR on alpine lakes would need to consider synergistic and antagonistic processes resulting from the pronounced climatic warming, which have the potential to modify the UV underwater climate and consequently the stress on aquatic organisms.     

Changes in ultraviolet absorbance and hence in protective efficacy against lipid peroxidation of organic sunscreens after UVA irradiation

Owing to the spectral distribution of solar UV, the UVA component of sunlight is now believed to be the main cause of photoaging and photocarcinogenesis and is much more effective than UVB in inducing peroxidative damage. Consequently, most skin care cosmetic products now include UVA filters in their formulations along with UVB filters. These modern sunscreens should provide and maintain their initial absorbance, hence protection, throughout the entire period of exposure to sunlight. However, not all UVA and UVB filters are sufficiently photostable. In this study, we examine the correlation between the photochemical degradation of sunscreen agents under UVA irradiation, with particular reference to the UVA-absorber 4-tert-butyl-4'-methoxydibenzoylmethane, alone and in combination with other organic UV filters (2-ethylhexyl 4 methoxycinnamate and 2-ethylhexyl 2-cyano-3,3-diphenylacrylate) and their ability to prevent UVA-induced lipid peroxidation. Since antioxidants are also added to formulations to deactivate free radicals generated during UVA exposure, vitamin E and the synthetic antioxidant, bis(2,2,6,6-tetramethyl-1-oxyl-piperidine-4-yl)sebacate, a nitroxide derivative, were also included in this study. By using simple in vitro tests, the results show that a decrease in spectral absorbance of the UV filters correlates in most cases with increased UVA-induced lipid peroxidation; this depends on the specific UV absorber analysed and also on whether they are alone or in combination. Furthermore, the combined presence or absence of antioxidants has a profound effect on this oxidative event. In particular, the nitroxide appears to be a more efficient photo-antioxidant than vitamin E. Similar experiments were also performed under natural sunlight and the results obtained did not differ substantially from those performed under UVA. The results presented and discussed in this work may help in understanding the effects of UVA/UVB absorbers and antioxidants upon the level of UV-induced ROS generated under UVA exposure and in natural sunlight which could be relevant for improving the photoprotection and efficacy of skin care cosmetic formulations.     

PHOTOREACTIVATION OF ICR 2A FROG CELLS EXPOSED TO SOLAR UV WAVELENGTHS

Abstract Exposure of ICR 2A frog cells to photoreactivating light (PRL) following irradiation with a fluorescent sun lamp (FSL) resulted in an enhancement in survival compared with FSL-irradiated cells incubated in the dark. Hence, pyrimidine dimers played a role in the killing of cells exposed to the UV produced by this source. However, when the light was passed through a series of filters to remove increasing segments of the wavelength region shorter than 320 nm, the effect of the PRL progressively decreased, demonstrating that non-dimer photoproducts play an increasingly important role in the killing of cells exposed to wavelengths approaching 320 nm. Cells were also exposed to 313 nm UV produced by a monochromator and it was found, once again, that the effectiveness of the PRL treatment depended on the filter the beam was passed through. These results indicate that for both FSL-produced UV and 313 nm UV emitted by a monochromator, that the critical photoproducts induced within the cell depend on the filter used in conjunction with the UV source.     

Photostability and phytotoxicity of selected sunscreen agents and their degradation mixtures in water

The study on the photostability of six UV filters in aqueous solution was combined with investigations on the phytotoxicity of the produced degradation mixtures. During the exposure to artificial sunlight over 72 h, the degradation of three of the UV filters evaluated was observed with half-lives between 20 and 59 h. The structural changes of iso-amylmethoxy-cinnamate (IAMC), ethylhexyl-methoxy-cinnamate (EHMC), and 4-methylbenzyliden camphor (4-MBC) occurred during irradiation were consistent with isomerisation and polymerization (IAMC and EHMC) whereas 2-ethylhexyl-4-(dimethylamino)benzoate (OD-PABA) was degraded. The analysis of the UV filters and their degradation products was performed by stir bar sorptive extraction (SBSE) followed by thermodesorption–gas chromatography–mass spectrometry (TD-GC-MS) or liquid desorption–liquid chromatography–mass spectrometry (LD-LC-MS). The phytotoxicological potential of the UV filters was examined in vitro by evaluating reproduction inhibition of the chlorophyte microalgae Scenedesmus vacuolatus. Excess toxicity was calculated by comparing experimental derived median efficiencies after log-logistic modeling to predict effects assuming narcotic mode of action. Benzophenone-3 (BP-3) showed 43-fold higher toxicity than theoretically predicted and a more specific mode of action was assumed. The other UV filters tested indicated toxicity in the range of modeled narcosis. For IAMC, EHMC, and OD-PABA the phytotoxicity of their photodegradation mixtures was followed over time. Phytotoxicity decreased directly with the reduction of the parent substance from the solution. Five of the tested UV filters do not represent a risk at least for algae. Octocrylen and 4-MBC were found to be photostable but few toxic to algae. EHMC, IAMC, and OD-PABA were fast degraded during UV radiation and the phytotoxicity of the corresponding degradation mixtures was low and decreased onward during exposure. Thus, for the UV filters studied, it could be confirmed that sunlight can account noticeably for decontamination and detoxification of contaminated water. However, due to its potential accumulation in combination with a specific mode of action, BP-3 may imply probable environmental risks at least to algae. This study emphasizes the need of a combined chemical and toxicological evaluation for a reliable risk assessment concerning degradation processes exemplified here for UV-protecting agents.     

PHOTOAGING EFFECTS ON SPECTRAL TRANSMITTANCE OF PLASTIC FILTERS

We examined the effects of ultraviolet (UV) radiation in combination with high levels of infrared (IR) radiation on the spectral transmittance of plastic filters. The biological action spectrum for damage to the human eye and skin changes dramatically in the 300-400 nm wavelength range. Cut-off filters used in this region to shape the spectrum of exposure sources are thus critical to the design of experiments which use broadband light sources. The changes in transmittance of three types of plastic filters were observed over an exposure period of 1000 h. One set of three filters was exposed mainly to UV radiation, while the other set was exposed to UV radiation plus IR radiation. Filters exposed to both UV and IR radiation showed spectral changes in their transmittance, while the filters exposed to UV only showed no measurable changes.     

Alternative methods to evaluate the protective ability of sunscreen against photo-genotoxicity

Numerous epidemiological investigations show that sunlight is carcinogenic to humans and that the use of sunscreen may be effective in decreasing the risk of skin cancer. The biological activity of a sunscreen is evaluated by its ability to protect human skin from erythema as represented by a Sun Protection Factor (SPF). We propose that the sunscreen's protective effect against sunlight-induced genotoxicity, including mutation, should also be taken into account. In this study we examined the protective ability of sunscreens against natural sunlight and UV-induced genotoxicity in Drosophila somatic cells. We prepared three kinds of sunscreen samples, each with an SPF value of 20, 40 or 60 and compared their protective activities with commercial sunscreens. When a sunscreen of SPF 20, 40 or 60 was pasted on the plastic cover of a petri dish in which Drosophila larvae were exposed to the sun or UV lamps, genotoxicity decreased as the SPF of the sunscreen increased, relative to levels of genotoxicity observed in samples without sunscreen. However, the protective abilities of sunscreens were unexpectedly not so different from each other. To reveal the relationship between the protective activity of sunscreen and the wavelength of light with which larvae were irradiated through the sunscreen, we measured the transmittance of light through the petri dish cover on which the sunscreen was pasted. Effective protection was demonstrated by removing components of light whose wavelengths were below 315 nm. We suggest, that the measurement of anti-genotoxic activity and the determination of the wavelengths of light transmitted through the sunscreen should be an alternative method for evaluating the effectiveness of a sunscreen.     

PHOTOBEHAVIOR OF EUGLENA GRACILIS: ACTION SPECTRUM FOR THE STEP-DOWN PHOTOPHOBIC RESPONSE OF INDIVIDUAL CELLS

Abstract—Light-induced behavioral responses of Euglena gracilis have been investigated in single cells by means of a video system coupled to an optical microscope. Light intensity-effect curves at different wavelengths in the near UV and visible range have been determined. From these curves the action spectrum for the step-down photophobic response of Euglena has been calculated. From a comparison with the results obtained using a population method by means of a phototaxigraph, it is concluded that a single photomotile reaction is responsible for cell accumulation, brought about by trapping in the light spot and possibly by phototaxis towards scattered light from organisms already in the light field.     

Development of a fully automated sequential injection solid-phase extraction procedure coupled to liquid chromatography to determine free 2-hydroxy-4-methoxybenzophenone and 2-hydroxy-4-methoxybenzophenone-5-sulphonic acid in human urine

2-Hydroxy-4-methoxybenzophenone and 2-hydroxy-4-methoxybenzophenone-5-sulphonic acid, commonly known as benzophenone-3 (BZ3) and benzophenone-4 (BZ4), respectively, are substances widely used as UV filters in cosmetic products in order to absorb UV radiation and protect human skin from direct exposure to the deleterious wavelengths of sunlight. As with other UV filters, there is evidence of their percutaneous absorption.This work describes an analytical method developed to determine trace levels of free BZ3 and BZ4 in human urine. The methodology is based on a solid-phase extraction (SPE) procedure for clean-up and pre-concentration, followed by the monitoring of the UV filters by liquid chromatography-ultraviolet spectrophotometry detection (LC-UV). In order to improve not only the sensitivity and selectivity, but also the precision of the method, the principle of sequential injection analysis was used to automate the SPE process and to transfer the eluates from the SPE to the LC system. The application of a six-channel valve as an interface for the switching arrangements successfully allowed the on-line connection of SPE sample processing with LC analysis.The SPE process for BZ3 and BZ4 was performed using octadecyl (C18) and diethylaminopropyl (DEA) modified silica microcolumns, respectively, in which the analytes were retained and eluted selectively. Due to the matrix effects, the determination was based on standard addition quantification and was fully validated. The relative standard deviations of the results were 13% and 6% for BZ3 and BZ4, respectively, whereas the limits of detection were 60 and 30 ng mL⁻¹, respectively. The method was satisfactorily applied to determine BZ3 and BZ4 in urine from volunteers that had applied a sunscreen cosmetic containing both UV filters.     

Both solar UVA and UVB radiation impair conidial culturability and delay germination in the entomopathogenic fungus Metarhizium anisopliae.

The entomopathogenic hyphomycete Metarhizium anisopliae has been used in programs of agricultural pest and disease vector control in several countries. Exposure to simulated solar radiation for a few hours can completely inactivate the conidia of the fungus. In the present study we determined the effect of exposures to full-spectrum sunlight and to solar ultraviolet A radiation at 320-400 nm (UVA) on the conidial culturability and germination of three M. anisopliae strains. The exposures were performed in July and August 2000 in Logan, UT. The strains showed wide variation in tolerance when exposed to full-spectrum sunlight as well as to UVA sunlight. Four-hour exposures to full-spectrum sunlight reduced the relative culturability by approximately 30% for strain ARSEF 324 and by 100% for strains ARSEF 23 and 2575. The relative UV sensitivity of the two more sensitive strains was different under solar UV from that under ultraviolet B radiation at 280-320 nm (UVB) in the laboratory. Four-hour exposures to solar UVA reduced the relative culturability by 10% for strain ARSEF 324, 40% for strain ARSEF 23 and 60% for strain ARSEF 2575. Exposures to both full-spectrum sunlight and UVA sunlight delayed the germination of the surviving conidia of all three strains. These results, in addition to confirming the deleterious effects of UVB, clearly demonstrate the negative effects of UVA sunlight on the survival and germination of M. anisopliae conidia under natural conditions. The negative effects of UVA in sunlight also emphasize that the biological spectral weighting functions for this fungus must not neglect the UVA wavelengths.     

THE RELATIVE IMPORTANCE OF VARIOUS ENVIRONMENTAL FACTORS ON THE VERTICAL DISTRIBUTION OF THE AQUATIC PROTOZOAN COLEPS SPIRALIS

Abstract— The vertical distribution of Coleps spiralis in a tertiary lagoon system was observed over a period of 18 months. Water samples were taken from the surface, middle and bottom of the lagoons and examined to determine the number of Coleps present. Various external and internal environmental factors (i.e. light, temperature, wind, etc) were investigated to determine which might be important in influencing the vertical positioning of Coleps in nature. Irradiance factors (both total solar irradiance and the UV-B component (λ= 320–280 nm) of sunlight showed the highest correlation with the location of the animals. When irradiance was high, the animals were usually found near the bottom of the lagoon; when irradiance was low the animals were located more randomly throughout the water column. On the other hand, wind, cloud cover, temperature gradients and bacterial (food) gradients showed low correlation with location of the protozoan in the water.     

SEASONAL PHOTOSENSITIVITY OF BLEPHARISMA: THE ROLE OF TEMPERATURE

Red blepharismas (B. japonicum) in Pyrex test tubes exposed near noon to clear summer daylight are killed. If similarly exposed at dawn, they turn blue as the red pigment blepharismin is oxidized to oxyblepharismin. and they resist further exposure to daylight. Red blepharismas similarly exposed to sunlight at dawn in winter are killed. The experiments reported seek the reasons for the seasonal difference in photosensitivity and the way in which blepherismas survive winter. Red blepharismas (B. japonicum) exposed to visible and near ultraviolet (UV) radiation from two 4W coolwhite fluorescent lamps (5 Wm^-2; 2151ux) resist an 8h exposure between 15° and 34°C. turning blue. Blue and colorless blepharismas also resist 8h exposures to the light at 15° and 34°C. At 8°C both red and blue populations are killed, death appearing to result from deranged water regulation; colorless ones are not affected. Red blepharismas are killed by fluorescent light at 8° C even when the near-UV radiation is largely excluded by a Corning glass filter; blue and colorless ones are not. The reds are also killed at all temperatures by sunlight filtered through Pyrex glass if exposed near noon on a sunny day. At temperatures above 8° C they are not killed by direct sunlight passed through glass if exposed at dawn, but they turn blue. Blepharismas in fluorescent light divide at the same rate as controls in the dark, but they get smaller. When exposed to sunlight at dawn, at temperatures above 8°C. blepharismas in Pyrex test tubes containing stones or fruiting spikes of grass, hid in the shade of these objects, apparently by random movements. If exposed under similar conditions near noontime, the majority failed to find cover and were killed. Blepharismas survive in summer by avoiding sunlight, in winter by encystment. Colorless protozoans Paraineciurn multimicronucleatum, Colpidium colpoda and Spirostomum teres resisted killing in summer sunlight and with fluorescent light at all temperatures tested.