262 SENSATION AND THE SENSIFEROUS OEGANS. 



throwing off excessively attenuated films of their own 

 substance : and that these films, reaching the mind, ex- 

 cite the appropriate sensations in it. 



Aristotle did not admit the existence of any such 

 material films, but conceived that it was the form of the 

 substance, and not its matter, which affected sense, as a 

 seal impresses wax, without losing anything in the pro- 

 cess. AVhile many, if not the majority, of the School- 

 men took up an intermediate position and supposed that 

 a something, which was not exactly either material or 

 immaterial, and which they called an " intentional spe- 

 cies," effected the needful communication between the 

 bodily cause of sensation and the mind. 



But all these notions, whatever may be said for or 

 against them in general, are fundamentally defective, by 

 reason of an oversight which was inevitable, in the state 

 of knowledge at the time in which they were promul- 

 gated. What the older philosophers did not know, and 

 could not know, before the anatomist and the physiolo- 

 gist had done their work, is that, between the external 

 object and that mind in which they supposed the sensa- 

 tion to inhere, there lies a physical obstacle. The sense 

 organ is not a mere passage by which the " tenuia simu- 

 lacra rerum," or the " intentional species " cast off by 

 objects, or the " forms " of sensible things, pass straight 

 to the mind ; on the contrary, it stands as a firm and 

 impervious barrier, through which no material particle 

 of the world without can make its way to the world 

 within. 



