While cycling 140 miles last week on the C and O Canal, I had lots of time to think.  The trip took me 4 days, and it was quiet and peaceful.  Most of the time the only evidence of civilization was other riders or hikers, the occasional airplane overhead or the sound of a railroad train in the distance.  Otherwise it was like being alone in the forest. The trail, which runs parallel to the Potomac River, was constructed as a towpath along the Chesapeake and Ohio Canal to pull barges filled with lumber, agricultural products and coal, down the canal to market.   The almost flat towpath goes from Cumberland Maryland to Washington DC. The C & O Canal is full of natural scenery and wildlife.  I saw a herd of deer, a few snakes, Blue Herons, a Bald Eagle, some vultures, a fox and countless turtles.  It was the turtles, lounging in the sun at one of the many locks along the way, that made me think about the truth about being cold blooded. Those turtles were in the sun to keep warm, not because their blood is cold, but because animals that are “cold blooded” take on the temperature of their surroundings.  If it is warm outside, they are warm.  If it is cold they are cold.   A warm-blooded animal, such as the deer and fox I saw, maintain a steady body temperature, despite the temperature of their surroundings. If it is cold outside, or if it is warm outside, these “warm blooded “ animals maintain a steady temperature through metabolic means. warm-blood·ed (adjective) Relating to or denoting animals (chiefly mammals and birds) that maintain a constant body temperature, typically above that of the surroundings, by metabolic means.  Also known as homoeothermic. cold-blood·ed   (adjective) Relating to animals (mainly fish, amphibians, and reptiles) having a body temperature that changes according to the temperature of the surroundings   Also known as poikilothermic.