THE GENERAL CONDITIONS OF LIFE 289 



carps, which, after having been frozen solid, revived and moved about 

 actively upon being warmed before a fire, although in specimens 

 that were killed the intestines were so solid that they could be 

 removed as a single piece. Likewise, by careful warming Dumeril 

 revived frogs that had been frozen solid in water of 4° to 12°; 

 and Preyer ('80), who has collected considerable testimony 

 upon this subject, made the observation that frogs frozen solid 

 could be revived if their internal temperature had not reached 

 2'5° C. Romanes made similar observations upon Medusas {Aurelia 

 aurita), whose delicate jelly-like bodies were pierced by abundant, 

 fine ice-crystals. But all these statements are to be accepted with 

 some criticism. The fact is not to be doubted that these animals can 

 be actually frozen solid in ice and yet be revived by careful thawing, 

 but in all the observations it is not certain whether the living sub- 

 stance of the cells themselves possesses a temperature below 0° C. 

 As is well known, all cells produce a certain quantity of heat in 

 their metabolism, and as a result of this when they are frozen their 

 internal temperature is always slightly higher than that of the 

 surrounding ice. It is, therefore, possible that in all the 

 observations the living substance of the cells itself was not cooled 

 to 0° or below 0°. Hence, more exact investigations were needed 

 in order to decide the question whether the living cell itself 

 undergoes without harm cooling of its substance to or below 0° C. 

 Such experiments have been performed by Ktihne, and more 

 recently and in great detail by Kochs. 



Kilhne ('64) placed upon ice in a watch glass a drop of water 

 containing many amcBbae, and found that gradually, in proportion 

 to the cooling, the movements became slov/er and slower, until 

 finally they ceased altogether and the amcebae lay completely 

 motionless. If the drop were again brought to the usual room- 

 temperature, the movements would begin again ; the amoebae, 

 therefore, were still alive. But the result was different when the 

 drop was frozen. Then, even after warming, the amoebae remained 

 motionless and could not again be revived. 



More recently, Kochs ('90) performed very detailed experi- 

 ments upon frogs and water-beetles. He froze these animals in 

 glasses containing water. If the temperature was not very low, there 

 remained around the animals, surrounded by ice, a liquid mass of 

 water, the temperature of which was 2° below the zero-point, as 

 was shown by boring through the mass of ice. If, after boring, 

 this last layer of water was frozen, the animals could still be revived 

 by warming, provided that they had not been frozen longer than 

 five to six hours. By sawing through such a preparation it was 

 shown that the animals were not frozen solid internally. But, if 

 the experiment was extended so that the animals were thus 

 frozen, which was the case when they wore brought into cold 

 air of 4° C, all attempts at resuscitation were in vain. 



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