PHYSICAL PROPERTIES OF PROTOPLASM. 39 



but dissolve readily in ether and chloroform. Treated with 

 aqueous solutions of alkalies they are converted into soluble 

 soaps. 



Physical Relations. The appearance, consistency, etc., of 

 protoplasm have already been described ; but it still remains to 

 speak of certain of its other physical properties, and especially of 

 the manner in which its activity is conditioned by various physi- 

 cal agents. 



Non-diffasib'tlitij. Living protoplasm, like most of the vari- 

 ous proteid matters which it yields (p. 37), is indiffusible. It 

 will be seen eventually that osmotic processes play a leading rule 

 in the lives of plants and animals, since they are in large part the 

 means by which nutriment is conveyed to the living substance. 

 In view of this fact, the non-diffusibility of protoplasm as well as 

 of ordinary proteids is a fact of great significance. 



Relations of vital action to temperature. It is a general law 

 that within certain limits heat accelerates, and cold depresses, the 

 activity of protoplasm. We know that cold tends to benumb our 

 own bodies (provided they become really chilled), and in animals 

 the heart beats more slowly, the movements become sluggish or 

 cease, breathing becomes slow and heavy, in a word, all of the 

 vital actions become depressed, whenever the ordinary temper- 

 ature is sufficiently lowered. If we chill the rotating protoplasm 

 of Chara or NiteUa, the vibrating cilia of ciliated cells, or an 

 actively flowing A.mceba, the movements become slower, and 

 finally cease altogether. 



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 rap- 

 idly, and the protoplasm of Chara courses more swiftly. In the 

 winter months the protoplasm of plants and of many animals is 

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

 and stop growing ; many animals bury themselves in the mud or 

 in burrows, and pass the winter in a deep sleep, during which 

 the vital fires burn low and seem well-nigh extinguished. The 

 warmth of spring re-establishes the activity of the protoplasm, 

 and in consequence animals awake from their sleep and plants 

 put forth their leaves. 



