SENSATION 



exposed to physiological investigation. It is true that 

 here also the task of science is to reduce all the bio- 

 logical phenomena to physical and chemical laws. But 

 it can only discharge a part of this difficult task, as 

 the phenomena are too complicated, and their conditions 

 too little known in detail, to say nothing of the crudeness 

 and imperfectness of our methods of research. Yet, in 

 spite of all this, comparative and phylogenetic physiology 

 convinces us that even the most complicated of our 

 internal excitations, and particularly the mental activity 

 of the brain, depend just as much as the outer stimula- 

 tions on physical processes, and are equally subject to 

 the law of substance. This is, in fact, true of reason 

 and consciousness. 



In man and all the higher animals the stimuli are 

 received by the organs of sense and conducted by their 

 nerves to the central organ. In the brain they are either 

 converted into specific sensations in the sense-centres, 

 or conveyed to the motor region, where they provoke 

 movements. The conduction of stimuli is simpler in 

 the lower animals and the plants; the tissue-cells either 

 directly affect each other or are connected by fine threads 

 of plasm. In the unicellular protists the stimulus which 

 strikes one particular spot of the surface may be imme- 

 diately communicated to the other parts of the unified 

 plasmic body. 



We shall see in the course of our inquiry that the 

 simplest form of sensation (in the widest sense) is 

 common to inorganic and organic bodies, and thus that 

 sensitiveness is really a fundamental property of all 

 matter, or, more correctly, all substance. We may, 

 therefore, ascribe sensation to the constituent atoms of 

 matter. This fundamental thought of hvlozoism, ex- 

 pressed long ago by Empedocles, has lately been very 

 definitely urged, especially by Fechner. However, the 

 able founder of psycho-physics {cf. the Riddle, p. 35) 



295 



