a test sample card has a fluid passage network provided on both sides of the card to provide for maximum separation distance between adjacent growth wells . the card also has cored sections along its periphery adjacent the wells , which improve the flow of plastic during the molding of the cards . the cored sections control the formation of knit lines in the surface of the card and eliminate knit lines from forming that could potentially bridge adjacent wells . these features , singly and together , combine to produce a card that is essentially immune to cross - talk between adjacent wells , yet permit a greater number of wells in a card of given dimensions . improved bubble trap features are also provided for the card , including a bubble trap passage having a restriction formed therein . the restriction prevents air bubbles in the bubble trap from migrating back to the growth wells .