An association football (soccer) match is presided over by a referee, whom the Laws of the Game give full authority to enforce the Laws of the Game in connection with the match to which he has been appointed (Law 5). The referee is oftentimes assisted by two assistant referees, and sometimes by a fourth official.
Barfoed's test. Barfoed's test is a chemical test used for detecting the presence of monosaccharides. It is based on the reduction of copper(II) acetate to copper(I) oxide (Cu2O), which forms a brick-red precipitate.
Guaiac-based fecal occult blood test (gFOBT) One way to test for colorectal cancer is to look for occult (hidden) blood in stool. The idea behind this test is that blood vessels in larger colorectal polyps or cancers are often fragile and easily damaged by the passage of stool.