A new figure of merit for liquid scintillation counters, expressing their ability to separate two beta spectra and thus to determine the concentrations of each isotope is derived. This
SYNOPSIS. A multi‐unit automatic sampling device for investigation of microbial growth under a wide variety of conditions is described. The kinetics of asynchronous population growth for batch cultures of Tetrahymena pyriformis (W) at several temperatures show that there are 2 distinct growth phases: an exponential ultradian growth phase that is strongly temperature dependent and a non‐stationary growth phase, the infradian phase, that shows little or no temperature dependence over the range from 15–27 C.
A photocell-controlled continuous culture device, a Nephelostat, is described that maintains a wide variety of cultures of microorganisms in balanced growth. This Nephelostat controls concentrations of bacteria within 3% over a cell concentration range of 106 to 109 cells per ml. Growth rates are recorded so that changes in the growth rate are observed over small increments of time. Spontaneous and caffeine-induced mutation rates of two strains of Escherichia coli were compared under Nephelostat and chemostat conditions.
An automatic, transistorized nest and burrow monitor is described which is low in cost, portable, self—contained and weather—proof. Each unit monitors 4 locations to a diameter of 32 m, each animal up to 1 m from its detector. Permanent weekly records are provided for each channel. Gamma rays from a tag on the animal are detected by miniature GM tubes. These are presented as counts on small, electric—pen recorders. While any gamma—emitting radionuclide can be used, certain ones are recommended by reason of their half—lives, gamma energies, and low radiation dose of the animal.
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