1 5 6 NA TURE OF SENS A TION. 



but until we have an accurate knowledge of its intimate 

 structure, we can only guess as to the change produced 

 upon the ultimate ramifications of the nerves. And until we 

 have discovered precisely how this change is propagated to 

 the centres, and made evident to us, it is indeed difficult to 

 understand how we are to give an adequate explanation of 

 what we mean by " sensation." It is not very probable 

 that we shall learn very much about the changes occurring 

 in sensitive organs until we thoroughly understand the 

 structure of these, and have conclusively demonstrated the 

 manner in which the terminal expansions of the nerves are 

 arranged, and have ascertained precisely how these terminal 

 expansions are temporarily affected by external agents. 

 Then we should be in a position to discuss how the altera- 

 tions effected in the terminal apparatus probably acted upon 

 part of the " organ of the mind," which is separated by a 

 great distance from the peripheral sensitive organs, and is 

 very close to " us ;" in other words, how the temporary 

 change induced in the sensitive organ was rendered evident to 

 the consciousness. But, unfortunately, not one link of this 

 chain of events has been adequately investigated ; not one 

 of the several series of changes that are undoubtedly pro- 

 duced in peripheral organ, nerve fibre, and central nerve 

 organ, has been fully elucidated. 



There is, indeed, the widest difference of opinion con- 

 cerning the change that actually occurs when the very 

 simplest nerve organ or nerve tissue " acts" and much yet 

 remains to be ascertained by investigation in this part of 

 the enquiry which is but preliminary and only introductory 

 to the question concerning the changes that occur in sen- 

 sation. If, therefore, a complete philosophy is to be based 



