ii LIVING MATTER 45 



The most rudimentary forms of consciousness, and as such the 

 most widely dispersed (common, it may be, to all living beings), are 

 represented by the phenomena of Sensibility, taken in the true 

 psychological and not in the metaphorical sense which is invari- 

 ably intended by physicists in speaking, e.g. of the sensibility of 

 the balance, galvanometer, or thermopile. 



Certain physiologists, including Claude Bernard, have con- 

 sidered sensibility to be the highest form, or evolutionary product, 

 of excitability, i.e. of the physiological property common to all, 

 even elementary, organisms of reacting to stimuli according to 

 their nature. This, however, is either to disallow the psychical 

 import of the word sensibility, or to admit as a fact that which is 

 wholly inconceivable, i.e. the emergence of any psychical pheno- 

 menon even in the form of vague internal sensations from 

 simple molecular movements. According to our physiological 

 concepts, sensibility and excitability do but express the same thing 

 from two different standpoints. " Excitability is for us sensibility 

 expressed in a verbal symbol suggested by external observation ; 

 sensibility is the same excitability expressed in a verbal symbol 

 derived from introspection. If we denote by excitation and 

 sensation the effects corresponding, respectively, to excitability and 

 sensibility, then excitation is the objective or material aspect 

 of sensation ; sensation is the subjective or psychical aspect of 

 excitation " (Luciani, 1892). 



This is merely a formal statement of the fundamental hypo- 

 thesis of psychophysics, viz. that psychical phenomena are the 

 correlatives of physiological phenomena, and express the aspects' 

 under which the latter surge up in consciousness, and form its 

 content. From the objective standpoint, psychical phenomena 

 also must be regarded as so many forms of excitation, determined 

 by the metabolism of the protoplasm, which is the common physio- 

 logical basis of all vital phenomena. 



III. In fulfilling the functions of nutrition, reproduction, 

 excitability, and sensibility, all plant and animal organisms are 

 subject to two laws, which to a certain extent are antagonistic, the 

 Law of Heredity, and the Law of Variation. The first represents- 

 the principle of Stability, the second the principle of Evolution. 

 Neither the one nor the other are to be understood in an absolute 

 sense, since they are mutually exclusive, but it is extremely 

 difficult to fix the precise limit between stability and variability,. 

 as appears from the history of biological science. 



Until some half-century ago the mind of most naturalists 

 was dominated by the law of stability, Fixity of Species being 

 a dogma, solemnly proclaimed by Linnaeus in his famous 

 aphorism " Species tot sunt quot diversas formas ab initio produxit 

 infinitum Ens" (Pliilosophia botanica, 1751). 



A little more than a century later, in 1859, the publication of 



