concept put forth in his book I Dare You, in which he proposed that four key components in life ("Physical", "Mental", "Social", and "Religious") need to be in balance, and one area was not to develop at the expense of the others. In 1921, the design inspired the design of feed that was pressed in cubes, called "checkers". See also Louisville sewer explosions Ralcorp Purina Mills References External links Purina Mobile Website Cargill's Purina division (international animal feed brand) Agribrands Purina Canada Inc. (Canada animal feed brand) Purina Mills Poultry Nutrition Purina iPhone App Purina BlackBerry App 01 Conglomerate companies of the United States American companies established in 1894 Food and drink companies established in 1894 Food and drink companies disestablished in 2001 1894 establishments in Missouri 2001 disestablishments in Missouri Dog food brands Cat food brands Nestlé brands 2001 mergers and acquisitions Defunct manufacturing companies based in Missouri