178 SECRETS OF EARTH AND SEA 



material of living things, which we call " protoplasm," 

 and most other chemical changes are thus arrested or 

 suspended. The most striking exception is that of the 

 most active of all elements, the gas fluorine, which 

 becomes a liquid at 210 degrees below zero centigrade, 

 and in that condition attacks turpentine if brought into 

 contact with it at the same low temperature with ex- 

 plosive force. Even solid fluorine combines with liquid 

 hydrogen with violent explosion. It seems certain, how- 

 ever, that elements or chemical compounds brought into 

 the solid (not merely liquid) condition by extreme cold 

 cannot act chemically upon other bodies in the same solid 

 condition, even when they would at normal temperatures 

 so act with the greatest readiness, because they are then 

 either liquid or gaseous. 



The conception of an arrest of the changes in 

 organisms, which we call life, followed by their re- 

 sumption after a greater or less interval of suspense, 

 was long ago suggested and discussed before we had 

 knowledge of the action of low temperatures. The 

 winter-sleep of some animals and the "comatose" con- 

 dition sometimes exhibited by human beings had led to 

 the notion of " suspended animation." But a careful study 

 of hybernating animals and of human instances of pro- 

 longed "coma" satisfied physiologists nearly ico years 

 ago that the processes of life — the beating of the heart 

 and the respiration — were not actually and absolutely 

 suspended in these cases, but reduced to a minimum. The 

 chemical processes connected with life were still very 

 slowly carried on. 



Again, a great deal of interest and discussion was 

 excited in the last century by the drying up of delicate 

 yet complex aquatic animalcules, such as the Rotifers 

 (the wheel animalcules described in our last chapter) 

 and Tardigrades (bear animalcules), and the fact that 



