THE HISTORY OF THE SUBJECT 9 



upon the kind of stimulus acting upon them. Johannes Muller, 

 grasping the idea hidden in this presentation, transformed it into 

 a clear and fundamental conception. Already in the work written 

 in his early years treating of optical illusions he says:^ "It is 

 immaterial by which means the muscle is stimulated, whether 

 by galvanism, chemical agents, mechanical irritation, inner organic 

 stimuli or sympathetic response from quite different organs; 

 to every means by which it is stimulated and an effect pro- 

 duced, it responds by movement. Movement is, therefore, the 

 effect and the energy of the muscle at the same time." "Thus 

 it is throughout with all reactions in the organisms." "The sensory 

 nerve, responding to any stimulus of whatever kind, has its 

 specific energy; pressure, friction, galvanism and inner organic 

 stimuli produce in nerves of sight that which is peculiar to them, 

 light sensation; in the nerves of hearing, that which is peculiar 

 to them, sound sensation; and in the nerves of touch, touch 

 sensations. On the other hand, everything which affects a secre- 

 tory organ produces change of the secretion; that which affects 

 the muscle, movement. Galvanism is not superior to any other 

 methods, of whatever kind, which can bring about stimulation." 

 And in his handbook of physiology Johannes Muller'^ formulates 

 the law of specific energy for the sensory structures briefly in the 

 following words : "The same external factor produces different 

 sensations in the different senses according to the nature of each 

 sense, namely, the sensation of the particular sensory nerves; 

 and the reverse: the characteristic sensations peculiar to every 

 sensory nerve can be produced by several internal and external 

 influences." This doctrine of the specific energy of the sense 

 substance possesses an importance which extends far beyond the 

 domain of the physiology of stimulation, for it forms the basis 

 on which the whole theory of human knowledge, must be built 

 up, no matter how it may be constructed in detail. 



As Johannes Muller already clearly emphasizes, it is here not 



1 Johannes Muller: "Uber die phantastischen Gesichtserscheinungen. Eine physiolo- 

 gische Untersuchung mit einer physiologischen Urkunde des Aristotles fiber den 

 Traum, den Physiologen und den Arzten gewidmet." Coblenz 1826. 



2 Johannes Muller: "Handbuch der Fhysiologie des Menschen fur Vorlesungen." 

 Coblenz 1837. 



