Abstract
Krueger and Northrop 1 were the first to undertake the study of bacteriophage action from a quantitative point of view. Based on extremely elaborate technical procedures, involving frequent and separate enumeration of bacteria and of bacteriophage throughout each experiment, they concluded that production of phage was proportional to a power of bacterial growth and that lysis set in almost explosively at the moment when phage/bacteria ratio attained a definite critical value. It would appear that according to their result the time required for lysis of a given bacterial concentration is proportional to the dilution of phage. Other conditions being constant, the strength of any 2 phages can be compared by noting the relative length of time necessary for reduction of a constant concentration of bacteria to an arbitrary end point.
The present paper is not intended to add anything new to the mechanism of bacteriophage action, but rather to present an accurate though considerably simpler device for attacking the problem from the same viewpoint. The apparatus used is a Pulfrich photometer which works on the principle of the Tyndall phenomenon, so that for a given bacterium, the number of organisms per cc. can be read off directly and quickly and is expressed in terms of percentage of a given standard. Very minute particles, namely, phage or protein particles, liberated during the process of dissolution of bacteria present a very weak Tyndall phenomenon and do not, therefore, affect the readings. Provided the bacterial suspension is not so thick as to interfere with penetration of light, the accuracy of readings obtained approached ±0.5% of the given standard, disregarding slight variations in the size and thickness of the tubes used.
The phage used throughout the experiment is from d'Herelle's laboratory and has been in our stock since 1927.
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