286 PHYSIOLOGY OF MUSCLES AM) NKRVES. 



qiKtte irrilnitfx, according to which there is such a 

 sufficient irritant for each sense-nerve, that is, an 

 irritant in its nature adapted to the nature of the 

 sense-nerve, and that this was alone able to excite it. 

 We kii'i\\- now that this is not true. Yet the expres- 

 sion maybe used to indicate the irritants which are 

 especially able to act on the terminal organs of the 

 nerves. 



In the same way we may look upon the idea of 

 so-called specific energies of the sense-nerves, if by 

 this it is intended to express any character of tin- 

 nerves, as disproved. But we must ascribe specific 

 energies to the individual nerve-cells in which the sen- 

 sations are originated. It is these alone vJiich ar- 

 able to produce in us different kinds of sensation. If 

 all the nerve-cells of the sensations were alike, sensa- 

 tions could indeed be elicited in us by the influence 

 of the outer world on our sense organs ; but these 

 would only be of one and the same kind, or at most it 

 could only be in the strength of (his one undefined 

 .-.nsation that differences would be perceptible. There 

 may be animals which are only capable of >uch a >in^le 

 undefined sensation, their nerve-cells hein^ all alike 

 ami not yet differentiated. Such animals would be 

 able to form a conception of the outer world as 

 distinguished from their o\\n bodies, that is, they 



Would be ;ible to c\,i|ve self-rolisciollslle-- : but the\ 



would not be able to attain a knowledge of the ]>r- 



in the outer \\orld. The development of -ndi 



knowledge in us i- great ly a-si>i ed by a comparison 

 of the different impressions brought about by the 

 different or^m- of the senses. A body presents itself 

 to our eye as occupying a certain .-pace, being of a 



