Frozen But Not Forgotten


100_2892Not long ago, on a warm February afternoon, I found myself sitting on a fallen log deep in the woods after having spent the morning searching for animal tracks, a form of entertainment that can keep me busy for hours.  I got a fairly late start, about 9 am on this cold morning.  Not unlike many February days the afternoon wind shifted to the south and a warm breeze started to blow in.  By about one thirty the temperature was in the low forties. I was working up a sweat climbing up this hill and descending down the next hill in search of wildlife sign where none could be found due to the hard frozen snow cover.   As I sat there resting I found myself appreciating the silence of the winter woods.  The quiet tells a story of nature at rest. 


To the east, not too far off in the distance I started to hear a chirping sound.  At first I thought it was some sort of bird, but I couldn’t place the call.  I stood up and walked about 100 feet towards the direction of the sound when I heard, again, the same low-tone chirping.  Not too far in the distance I could see an area of melted ice near the edge of a shallow vernal pool.  There was little doubt in my mind that the unfrozen area was spring fed from ground water with a temperature well above 32 degrees.  The chirping was not a bird at all, but the solo chorusing of a confused wood frog thinking spring had arrived. 


There is little question that a chorusing wood frog would seem out of place to almost anyone in this cold, mostly frozen environment.  As I puzzled about this it all began to make sense to me.


Wood Frogs are very unique creatures, even for the amphibian world.  Many amphibians bury themselves in the dirt or mud as the first hard frosts arrive.  As the frost goes deeper into the ground, most of these creatures sense the cold and dig themselves in a little bit deeper to avoid temperatures that will remain consistently below freezing.  By the middle of winter most of these amphibians (and many reptiles) find themselves a few feet into the ground in a deep sleep known to most of us as hibernation.  But there are a few amphibians like the wood frog and spring peeper that have developed special mechanisms to deal with the cold weather. 


The wood frog will bury itself under a thin layer of the forest floor or leaves shed from nearby hardwoods as winter approaches.  At the first sign of a hard frost this frogs’ skin will sense freezing and relay a message that releases adrenaline into the cardiovascular system of the frog.  The adrenaline activates enzymes in the liver that converts glycogen to glucose.  The living cells of the frog become consumed with glucose.  On the inside of the cells the glucose is converted to glycerol, an alcohol-like substance that acts as antifreeze.  On the outside of the cells glucose and special proteins osmotically remove water from the living cell wall.  In this way the voids between the cells freeze but not the actual living cells.  The end result is that no important tissue is damaged by the frost within the frogs’ body. This frozen state, in combination with the hibernating frogs’ very slow metabolism and respiration, allow the frog to survive on what limited energy reserves it has stored for the duration of the winter.


Even a slight change in their overall environmental temperature can unfreeze the frog and bring it back to life.  On this day the combination of the ice thaw near the spring feeding the vernal pool and the sudden spring like temperatures created the perfect situation for the wood frog to come back to life.  No doubt it was refrozen back into a state of suspended animation by nightfall. 


Modern science has taken note of the wood frogs’ unique ability.  Dr Kenneth Story of Carleton University and Dr. Boris Rubinsky of U.C. Berkeley have studied the freezing and osmotic process in wood frogs to help cryopreserve living organs, a process that could prove to be very helpful in preserving donor organs for longer periods of times than is now possible.  Their research has revealed that cellular dehydration is the key factor that will determine whether or not cells can survive this freezing process.  Successful pilot programs involving rat organs show great hope for the successful long term storage of human organs in the near future.


Later that afternoon, as the sun hung low in the southwestern sky and an evening chill began to settle in, I headed back through the woods to a warm place that I call home.  On the way, as the dark began to obscure the shadows of the naked winter trees, I think about today’s revelation.  It is comforting to me that humans can borrow from the wisdom and riches of nature to benefit all of mankind.  But I am puzzled, and somewhat horrified, as to why we aren’t cognizant of the problems we create when we fail to respect the natural world when we pollute and destroy the very life from whence we come.


This night’s journey home will be very dark, indeed.


Originally written in March, 2004.



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