The embodiment shown in FIG 4 is characterized by the application to the exterior of the tube 12 of a silver or other oligodynamically active metal in a powdery form ranging in {HEAD ~ particle size} between 200 and {TAIL ~ 300 mesh} 
between
The embodiment shown in FIG 4 is characterized by the application to the exterior of the tube 12 of a silver or other oligodynamically active metal in a powdery form ranging in { HEAD ~ particle size } between 200 and { TAIL ~ 300 mesh }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL