An Improved Arrangement for Bacteria-Retaining Filters.

Abstract

Attention has lately been redirected to the importance of adsorption in filtration through bacterial filters 1 ; however, if filtration is prolonged, the adsorbing surface may become saturated and substances at first retained may appear in the filtrate. The range of particle size from the smaller filterable viruses to the ordinary bacteria, on the other hand, is a critical zone in which mechanical retention plays an increasingly important and finally a determinative role. 2 Certain ultramicroscopic viruses may pass the more porous filters in almost undiminished concentration, others in greatly reduced concentration. The visible microorganisms pass the filters only in sufficient numbers to inoculate the filtrate, and only pass at all when certain attributes of the microorganism (e. g., small size, motility, flexibility), or the circumstances of the filtration are especially favorable.

It does not suffice, then, to report that a certain virus is or is not filterable through certain filters. 3 The circumstances must also be known. Incomplete recording of the details of procedure, together with diversity of filtration methods and lack of exact experimental control of the filtration technique, have often introduced needless confusion into the literature on filterable viruses.

The arrangement shown in the accompanying figure offers advantages in point of control over the filtration process, as well as in convenience of operation. The reduced filtration pressure is shown by the manometer. The filtrate is received into a graduated vessel. Filtration may be interrupted at any moment by stopping the suction pump and opening the stop-cock on the trap to equalize pressure. Measured volumes of filtrate are then inoculated sterilly into any desired number of culture tubes through the delivery tube with protective apron. The pinch-clamp is released, the stop-cock closed, and suction is continued until another volume of filtrate is collected, and so on indefinitely.