{HEAD ~ 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 {TAIL ~ particle size} between 200 and 300 mesh 
{ HEAD ~ 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 { TAIL ~ particle size } between 200 and 300 mesh
HEAD HEAD HEAD HEAD HEAD HEAD 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 TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH