Assertion : Volume and fluidity of intestinal contents have increased in a person.
Reason : The person drank sea water.
If sea water is drunk, its Mg2+ ions increase the solute concentration in the intestinal lumen because Mg2+ is absorbed very slowly. On the contrary, Mg2+ draws water from the blood to the intestinal lumen by osmosis. So, water is not gained, but is lost from the blood on drinking sea water. Thus, there occurs increase in the fluidity and volume of intestinal contents, in the same way this consequently stimulates intestinal peristalsis and evacuation of fluid faeces.