1895] MICROSCOPICAL JOURNAL 305 



in watching these lowliest living beings it is found that 

 they discriminate and choose, going freely into some 

 portions of their liquid world and withdrawing from 

 other i3ortions. If some drug which is unusual, or we 

 must believe disagreeable, is added to a part of the wa- 

 ter they withdraw from that part. It seems to have the 

 same effect as disagreeable odors on men and animals. 

 On the other hand, there are substances which attract, 

 and into the water containing these they enter with 

 eagerness. Strange is it too that as proved by experi- 

 ment, if an unattractive substance is used, and also one 

 on the other side that has been still more attractive, the 

 less disagreeable is selected, the less of two evils is 

 chosen. 



As man, the horse, dog and many other animals adapt 

 themselves gradually to temperatures either very cold or 

 very warm, and that too by a change in their heat-regu- 

 lating power rather than by a change of hairy or other 

 clothing, so these lowly organisms are found in nature 

 in water at temperatures from near freezing up to 60° — 

 80° C; a point approaching that of boiling water. It 

 may be answered that each was created for its place; 

 but by means of a microscope and a delicate thermostat, 

 to be certain of every step and to see all the results. Dr. 

 Dallinger, tlirough a period of seven years, accustomed 

 the same unicellular organism and its progeny to vari- 

 ations of temperature from 15° — 20° C; i. e., about the 

 temperature of a comfortable sitting-room, up to 70°C. 

 For those at the cooler temperature it was death to in- 

 crease rapidly the temperature 10° and for those at the 

 higher temperature it was equally fatal to lower the 

 heat 15° — 20°, their original normal temperature. These 

 examples seem to show that it is one of the fundamental 

 characteristics of living substances, whether in complex or 

 simple forms, to adapt themselves to' their environment. 



There is another fact that the microscope has revealed 



