Perhaps the best mode of studying the density of the kidney filter for a short time is to produce a hydronephrotic sac by tying the ureter. In this way, all the bacteria that are excreted during a short period can be retained. For longer periods of time this would not necessarily hold true, as bacteria are rapidly absorbed from a closed sac and can be early demonstrated in the circulation, as shown by Magoun1 and others. If no growth of bacteria in such a closed sac occurred, it is conceivable that there might be partial sterilization by the production of a hydronephrotic sac.
If it is true, as maintained by Biedl and Kraus,2 Rolly,3 David and McGill,4 and others, that bacteria are being excreted by the kidney in large number during the first hours after intravenous injection, then surely they should be constantly present in hydronephrotic