a device for filtering a parenteral solution immediately before it is infused into a patient &# 39 ; s vein . the device has a hollow housing containing a &# 34 ; depth &# 34 ; filter membrane of nonfibrous hydrophobic material having randomly connected stacked passages of from 10 to 40 micron size through the filter . after the filter membrane has had one surface in contact with the parenteral solution for a period of 15 to 60 seconds while passing only a minute amount of liquid it is then manually tapped to send a shock wave through the filter . this shock wave unexpectedly causes the hydrophobic filter to freely pass liquid and filter out more than 90 percent of all particulate matter of 5 micron size and larger from the parenteral solution . the large pore hydrophobic filter membrane can perform these filtering efficiencies with a very small , thin disc - shaped membrane of approximately 1 / 4 inch effective diameter .