Microencapsulation and Artificial Cells : Humana Press : 9781461296010 : 1461296013 : 08 Oct 2011 : Early studies by Pendleton and West (1) in 1932 demonstrated that urea moved from the blood into the small intestine in uremic dogs. In 1946, Twiss and Kolff (2) showed in uremic patients that urea could be removed when an isotonic solution was perfused through an isolated in­ testinalloop. Since these early studies had demonstrated the presence of urea and its removal from the gastrointestinal tract, Yatzidis (3) in 1964 investigated the use of activated charcoal for the removal of uremic wastes from the intestinal tract. In addition to Yatzidis' studies with char­ coal, other investigations with charcoal have been unable to confirm any significant reduction in serum levels of urea, creatinine, uric acid, or guanidines (4,5) via this approach. At the same time that Yatzidis proposed the use of charcoal for re­ moval of nitrogenous wastes from the intestinal tract, he also proposed using