Abstract
The following experiments, which are intended as preliminary steps in a study of some of the effects of cathode rays upon cells. provide data for a statistical analysis of the rate of killing of cultures of B. coli, of Staphylococcus aureus and of B. aertryke.
The cathode rays have been obtained from a Coolidge type electron tube operated at a voltage of approximately 200 K.V. Small numbers of the organisms under investigation were evenly spread upon the surfaces of agar plates and known areas were exposed for different lengths of time to the electron stream. After incubation, counts were made of the numbers of colonies growing out in these areas and in similar standard areas shielded from radiation. The ratios of the bacterial colonies in these areas are survival ratios.
A picture of the physical consequences of an electron absorption in a bacterium will be provided by remembering that whenever a fast moving electron is absorbed in matter, some of its energy will be emitted as X-rays but the major part will produce a large number of charged ions within a very small volume. In the present experiments this volume is probably less than 0.001 mm.3 and within it an absorbed electron gives rise to upwards of 10,000 ions. It is natural to attribute the destructive action of cathode rays to the chemical and physical changes resulting from this ionic shower.
By estimating both the number of electrons which strike a bacterium in unit time and the absorption coefficient of these electrons in the bacterium, it is possible to analyse the observed survival ratios by the usual methods of probability theory. Such an analysis will show how many electrons may be stopped by a single bacterium before death results.
Get full access to this article
View all access options for this article.