During the past fifty years, many investigators have studied the bactericidal activity of ultra violet light, but a review of their reports shows that little has been learned about many essential factors in the reaction. There have been few contributions to a knowledge of the quantitative relations involved. Little precise information is available on differences in resistance of individual bacteria to monochromatic light and the consequent reaction curve of large numbers of organisms; on the effective range of ultra violet frequencies; on the relation between incident and absorbed energies at various wave lengths; on relations between time and intensity; on the temperature coefficient; on the action of polarized light; or indeed on any of the factors essential to the reaction on which an examination of its biophysical significance must be based.But the ultimate object of the present study has not been simply to determine a set of coefficients for the bactericidal action of ultra violet light. This particular reaction was chosen for study because less individual variation is to be expected among bacteria than among higher forms of life. They are easily handled in quantity, and the death or survival of microorganisms provides a clearcut endpoint which may be observed and statistically recorded with unusual accuracy for biological material. They seemed to afford the best available opportunity for a quantitative study of an effect of certain frequencies in the ultra violet on protoplasm: with the prospect that the reaction of the bacterial cells might open leads for further studies on higher organisms.It is obvious that in such work a considerable number of factors 231

In this study of the bactericidal action of ultra violet light the first paper (1) described the reaction of an 18 hour culture of Staphylococcus aureus to monochromatic radiations. It was shown that the course of the reaction among large numbers of organisms was approximately the same at each wave length studied but that widely different incident energies were required at different wave lengths to produce these similar effects.The second paper (2) discussed the limits of the bactericidal zone, showed that the reaction had a low temperature coefficient, (approximately 1.1), gave evidence that within the variations of the methods used no significant errors were introduced by differences in the measured intensity of the source or in the hydrogen ion concentration of the medium, and indicated that plane polarization of the incident light had no effect upon the reaction.The present paper deals with the absorption of ultra violet light by intact bacteria. A final paper in this series will discuss structural and chemical units of bacterial protoplasm that may prove to be involved in the reaction which results in the organism's death. Incident Energy Relationships at Various Wave LengthsText- fig. 1, reproduced from the first paper of this series, shows that although the course of the bactericidal reaction was approximately the same at each wave length studied, these similar curves were found at very different incident energy levels at different points in the ultra violet spectrum.

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The first paper of this series (1) dealt with the reaction of an 18 hour culture of Staphylococcus aureus to monochromatic ultra violet energy, and it was shown that the course of the reaction was the same at each wave length studied. A consideration of certain factors, such as age and metabolic activity, in the resistance of individual bacteria gave a partial explanation of the course of the reaction among large numbers of organisms. But very different total incident energieswere required at different wave lengths to produce these similar effects and an examination of energy relationships and the spectral limits of the bactericidal region was reserved for later consideration.Before taking up the relation between incident energy and the coefficient of light absorption at different wave lengths, a relation essential to an analysis of the structural elements in bacteria which are affected by light, and to the nature of the resulting reactions, it seems desirable to estimate the effect on the reaction of various conditions of experiment and certain factors in the environment for which due allowance must be made.The present paper, therefore, will deal with:(1) The relation between the intensity of the incident energy and the time required for bacterial destruction (the Bunsen-Roscoe Law).

1. A meningococcus vaccine suspended in salt solution has been given subcutaneously as a prophylactic to about 3,700 volunteers in three injections of 2,000 million, 4,000 million, and 4,000 or 8,000 million cocci at weekly intervals. 2. These doses rarely caused more than the mildest local and general reactions. Exceptionally a more severe reaction emphasized the presence of an unusual individual susceptibility to the vaccine. In such instances the symptoms were in part those of meningeal irritation and sometimes simulated the onset of meningitis. 3. Specific meningococcus agglutinins have been demonstrated in the blood serum of vaccinated men as compared with normal controls. 4. Moreover, agglutinins have been demonstrated in the blood serum of chronic carriers of the meningococcus. Evidence is thus brought forward that the relative immunity of chronic carriers to epidemic meningitis may be due to the presence of specific antibodies in the blood stream.