DIVISION II 

 PHYSIOLOGY (^ 



THE object of Physiology is to describe the phenomena of life, to 

 study their dependence on external factors, and so far as possible to 

 trace them back to their CAUSES. Physiology, like Chemistry and 

 Physics, is concerned with inquiries into the causes of what takes 

 place. It must, however, also take into consideration the significance 

 to the organism of what happens. In its methods as well as in its 

 problems Physiology agrees with Physics and Chemistry ; its methods 

 are EXPERIMENTAL. 



The main results of physiological investigation are the following : 



1. There is no fundamental distinction between the vital pheno- 

 mena of animals and plants. This is not surprising, since plants 

 and animals are only morphologically distinct in their more advanced 

 representatives. In the physiological sphere it becomes more and more 

 clear, as investigation proceeds, how similar the course of life in the 

 two kingdoms is. The physiology of organisms is thus really a single 

 subject. A text-book of botany has evidently only to give an account 

 of the physiology of plants, but, where this is useful, analogous pheno- 

 mena in the animal kingdom will be mentioned. 



2. In some respects the behaviour of the living plant does not differ 

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

 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. 



3. The ESSENTIAL PHENOMENA OF LIFE are strikingly different from 

 the processes met with in non-living bodies. They are intimately 

 connected with the protoplasm and depend on the peculiar fashion 

 in which this substance reacts to influences of the outer world, i.e. 



Upon its IRRITABILITY and CAPACITY OF REGULATION. 



(a) Irritability. In the reactions of the organism the con- 

 nection between the causal influence and the effect induced by it 

 is not so apparent as it is in chemical or physical processes. This 



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