322 Evolution and Adaptation 



to a change in the protoplasm of the individuals. It was 

 also determined that the acquired resistance was only very 

 gradually lost (after seventeen days' sojourn in cooler water). 

 The explanation of this result may be due, in part, to the pro- 

 toplasm containing less water at higher temperatures, for it 

 is known that while the white of egg (albumen) coagulates 

 at 56 degrees C. in aqueous solution; with only 18 per cent 

 of water it coagulates between 80 degrees and 90 degrees C. ; 

 and with 6 per cent, at 145 degrees C. ; and without water 

 between 100 degrees and 170 degrees C. 



It has long been known that organisms in the dry condi- 

 tion resist a much higher temperature. The damp uredo- 

 spore is killed at 58.5 degrees to 60 degrees C. ; but dry 

 spores withstand 128 degrees C. It is also known that 

 organisms may become acclimatized to cold through loss of 

 water, but we lack exact experimental data to show to what 

 extent this can be carried. 



There are also some experiments that go to show that ani- 

 mals may become attuned to certain amounts of light, but the 

 facts in this connection will be described in another chapter. 



Some important results have been obtained by accustom- 

 ing organisms to solutions containing various amounts of salts. 

 A number of cases of this sort are given by De Varigny. It 

 has been found that littoral marine animals that live where 

 the water may become diluted by the rain, or by rivers, sur- 

 vive better when put into fresh water than do animals living 

 farther from the shore. Thus the oyster, the mussel, and the 

 snail, Patella, withstand immersion in fresh water better than 

 other animals that live farther out at sea. The reverse is 

 also true ; fresh-water forms, such as Lymnaea, Physa, Palu- 

 dina, and others may be slowly acclimatized to water contain- 

 ing more salt. The forms mentioned above could be brought 

 by degrees into water containing 4 per cent of salt, which 

 would have killed the animals if they had been brought sud- 

 denly into it. Similar results have been obtained for amoeba. 



