Chapter I 

 INTRODUCTION 





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One of the most striking properties of living sys- 

 tems is their ability to modify their activities, not in 

 a continuous fashion, but in response to changes in 

 their environment. While responsiveness to external 

 variations is also shown by inorganic systems, the in- 

 duced changes of state are by no means so complex 

 and varied as those shown by living matter. 



A further characteristic of living matter is that in 

 many instances an extremely minute environmental 

 variation brings about a response in an organism, 

 which is out of all proportion to the magnitude of the 

 change in the environmental conditions which has 

 elicited the biological response. 



For example, the presence of 0.0000000249% 

 (about 1 part in 4,016,000,000) of copper sulphate in 

 water was found by Kanda (1904) to have a definitely 

 inhibitory effect upon the growth of seedlings of peas, 

 broad beans, and buckwheat. Mast (1928), working 

 with amoeba proteus, observed that when these pro- 

 tozoans are transferred from a hay infusion medium 

 to freshly distilled water, a large proportion of them 

 rapidly becomes inactive and markedly radiate in 

 form. Furthermore, the number of individuals which 

 attach themselves to the vessel walls is determined by 



1 



