Serendipity After the cold rush

I HAVE JUST finished reading Absolute Zero and the Conquest of Cold by Tom Shachtman, a fascinating history of the science of cold, which is not without its serendipitous episodes. For example, in 1892 the Scottish chemist James Dewar invented the vacuum flask, developed in order to store liquids, such as liquid oxygen, at very low temperatures. The hollow wall of the flask was evacuated so that no heat could be conducted through it. Its design was deliberate and elegant, so much so that Dewar was blinkered to the flask's commercial potential. He never considered using the so- called dewar flask to keep hot liquids hot.

Instead, it was left to a German glass-blower, who was manufacturing vacuum flasks for Dewar, to turn a piece of experimental apparatus in to an everyday product. For some reason that has been lost in the mists of time, the glassblower found himself stuck with some excess baby milk one evening. There being no other receptacle to hand, he placed the milk in a flask, and was surprised to find that it was still warm when he returned the next morning. He called his commercial product a "Thermos Flasche" or thermos flask.

An even more important example of cryogenic serendipity happened in 1912, when Clarence Birdseye went fishing in the sub-zero conditions of Labrador in Canada. Like the Eskimos, he would drop a line through a hole in the ice, haul out the fish and hoist it over his shoulder. Naturally, the fish froze, but Birdseye was astonished to find that the fish tasted fresh several weeks later when it was defrosted and cooked. In the past, when food had been frozen for storage, it tasted awful.

The original Captain Birdseye soon realised why his Labrador fish tasted so good. The key to success was quick freezing, caused by suddenly exposing the fish to an air temperature of -40C. Freezing leads to the formation of ice crystals within a fish's cells, but rapid freezing means that the crystals are all small. In contrast, previous freezing had been gradual, which resulted in large crystals - spiky structures that punctured cell walls, thereby destroying the quality of the food.

Nowadays we take frozen fishfingers for granted, and the challenge is not to freeze dead things and eat them, but rather to freeze dead things and then bring them back to life. Some cells are quite resilient, and for those suspended animation is simple. For example, sperm is stored in liquid nitrogen at -196C, which kills off only one third of the cells. Similarly, bone marrow tissue can be frozen and revived. This is vital for cancer patients who donate their own bone marrow, have it stored, and then have it returned to them to replace cells killed by chemotherapy. Whether a frozen brain could ever be revived is quite another matter.

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