A series of controlled physiological experiments investigates how cathartic agents produce purgative effects, focusing on saline laxatives and plant extracts. Using animal preparations, isolated intestinal loops, and local application to peritoneal surfaces, the author examines changes in intestinal secretion and motility, systemic influences such as renal secretion, and the modifying roles of divalent salts. Evidence is marshaled that calcium and barium alter or counteract the action of saline cathartics, and the monograph compares mechanisms across different compounds while detailing methods and results.