38 PROTOPLASM AND THE CELL. 



benumb our own bodies (provided the j become really cliilled), and ' 

 in lower animals the heart beats more slowly, the movements be- 

 come sluggish or cease, breathing becomes slow and heavy, — in 

 a word, all of the vital actions become depressed, — whenever 

 the ordinary temperature is sufficiently lowered. If we chill 

 the rotating protoplasm of Chara or Nitella^ the vibrating cilia 

 of ciliated cells, or an actively flowing A^noebay the movements 

 become slower, and finally cease altogetlier. 



On the other hand, moderate warmth favors protoplasmic 

 action. Benumbed fingers become once more nimble before the 

 warmth of the fire. In a hot room the frog's heart beats more 

 rapidly, cilia lash more energetically, the Amoeba flows more 

 rapidly, and the protoplasm of Cliara courses more swiftly. In 

 the winter months the protoplasm of j)lants and of many animals 

 is in a state of comparative inactivity. Most plants lose their 

 leaves and stop growing ; many animals bury themselves m the 

 mud or in burrows, and pass the winter in a deep sleej) {Jiiberna' 

 tion)^ during which the vital fires burn low and seem well-nigh 

 extinguished. The warmth of spring re-estabhshes the activity 

 of the protoplasm, and in consequence animals awake from their 

 sleep and plants put forth their leaves. 



But this law is true only within certain limits. Extreme 

 heat and cold are alike inimical to hfe, and as the temperature 

 approaches these extremes all forms of vital action gradually or ;> 

 suddenly cease. The limits are so variable that it is not at 

 present possible to formulate any exact law which shall include 

 all known cases. For instance, many organisms are killed at 

 the freezing-point of water (0° C); but certain forms of life 

 have withstood a temperature of — 87° C. {— 123° F.), and re- 

 cent experiments show that frogs and rabbits may be chilled to 

 an unexpected degree without fatal results. 



The upper limit is also inconstant, though less so than the lower. 

 Most organisms are destroyed at the temperature of boiling 

 water (100°C.), but the spores of bacteria have been exposed to 

 a much higher temperature ^vdthout destruction (120"— 125° C). 

 As a rule, protoplasm is killed by a temperature varying from 

 40° to 50° C, the immediate cause of death being aj^parently 

 due to a sudden, coagulation (p. 36) of certain substances in the 

 protoplasm. Thus^ if a brainless frog be gradually heated, 



