THE VITAL PROPERTIES OF THE CELL 



111 



FIG. 67. Orbitolites. A portion of the surface with its pseudopodia : .A undisturbed ; B 

 the whole has been stimulated by repeated shaking. (After Verwornlll. 24, Fig. 7.) This 

 is of importance to Rhizopoda in absorbing food. 



gradually shortens itself, a motion in which the neighbouring 

 threads eventually participate, the Infusorian is gradually drawn 

 into the centre of the protoplasmic mass, where it undergoes 

 digestion. 



V. Chemical Stimuli. A living cell is able to a certain 

 extent to adapt itself to chemical changes in its environment. For 

 this, however, one thing is most important, namely that the 

 changes should be made gradually, not suddenly. 



JEthdtiwn plasmodia flourish in a 2 per cent, solution of grape- 

 sugar, if the latter is added in gradually increasing quantities to 

 the water (IV. 35). If they were to be transferred straight from 

 pure water into this chemically different environment, the sudden 

 change would result in their death ; this would also occur if they 

 were to be suddenly placed back into pure water from the 2 

 per cent, sugar solution. It is evident that the protoplasm needs 

 time to adapt itself to its altered condition, probably by increasing 

 or diminishing the amount of water it contains. 



Marine Amoebae and Reticularia remain alive after the water 

 which contains them, in consequence of being in an open vessel, 

 has evaporated so much that it contains 10 per cent, of salt. 

 Fresh water Amoebae can gradually accustom themselves to a 4 

 per cent, solution of common salt, whereas, if they are suddenly 

 immersed in a 1 per cent, solution, they contract into balls, and in 

 time become broken up into glistening droplets. During the pro- 

 cess of adaptation to a new chemical environment, the individual 



