VI ABSENCE OF SENS A TION IN PLANTS 309 



a mechanical conception of the idea of will, as follows from 

 the explanation of will given on p. 223, I must strenuously 

 protest against his application of the word. I connect the idea 

 of will exclusively with nervous substance, or with the 

 nerve-plasma which represents it : will is not a property of 

 protoplasm, still less of matter in general, but a property of 

 nervous tissue, in most cases of definite nerve -cells — 

 the will is an acquired and inherited property. The nerve- 

 cells of the brain alone are capable of storing up external 

 influences, i.e. the action of stimuli, as experience, in such a 

 way as is required for voluntary action in the sense of the 

 " release of forces existing in a state of tension." The will 

 depends upon movement, as does the whole of mental life, 

 and life in general. Irritability and sensation likewise 

 depend upon motion, but sensation also is a property of 

 nervous substance, or of the nerve-plasma, is not possessed 

 by plants any more than by inorganic bodies ; but the latter 

 are also destitute of irritability, W'hich, however, is a property 

 of protoplasm. Inorganic bodies possess only the property of 

 combining together according to regular laws in consequence 

 of attraction and repulsion. Irritability is a fundamental 

 property of protoplasm; capacity for sensation, on the contrary, 

 is a property acquired by it. 



Haeckel's conception depends upon a quite arbitrary use 

 of the terms. It arises simply from the desire to find unity 

 in nature, even in the province of mental phenomena ; for it 

 appears indeed at first sight dualism to suppose that one 

 class of organisms is endowed with sensation and will, 

 another not. But this demand for unity has no justification 

 — it forgets the fact of the modification of the properties of 

 organic nature by the action of external stimuli, it con- 

 founds acquired powers with the fundamental properties of 

 matter. 



It is absolutely unnecessary and in contradiction to 



