SECTION II 

 PHYSIOLOGY 



Physiology is the study of life. Its ultimate object is to explain 

 the nature of life, but at present it has to rest satisfied with describing 

 the phenomena of life, and studying the influence of various factors 

 upon them. Physiology like chemistry and physics is concerned with 

 incpiiries into the causes of what takes place. It is thus distinguished 

 from oecology (p. 6), a study which also deals with the phenomena 

 of life ; this seeks for the purpose, or, better expressed, the uses to the 

 organism, of adaptations or of processes, and is thus a teleological 

 rather than a causal study. Since, however, every aspect or dis- 

 cipline of the science cannot be separately dealt with in a text-book, 

 this section will treat of oecological as well as of physiological prob- 

 lems. This is further justified by the fact that physiology and 

 oecology may and often have had a useful mutual influence. 



Since animals and plants are only sharply separable in their more 

 advanced forms, animal physiology and plant physiology must have 

 much in common. This fact emerges the more clearly when, on the 

 one hand, the animal physiologist concerns himself with the lower 

 animals, and, on the other hand, the vegetable physiologist studies the 

 processes of irritability. 



In some respects the behaviour of the living plant does not difter 

 from that of non-living bodies. In spite of the large amount of Avater 

 which it contains, the plant is as a rule solid, and has the physical 

 properties of such a body. Weight, rigidity, elasticity, conductivity 

 for light, heat, and electricity are properties of the organism as they 

 are of lifeless bodies. However important these properties may be to 

 the existence and the life of the plant, they do not constitute life 

 itself. 



The phenomena of life are essentially connected with 

 THE living protoplasm. No Other substance exhibits even similar 

 remarkable and varied properties, which we can compare to life. It 

 is especially characteristic of the organism that the reaction which 

 follows an external influence is a very complicated one. The con- 

 nection between the causal influence and the effect induced by it 



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