FROG: NERVOUS SYSTEM AND SENSE ORGANS 79 



us infers from the behaviour of other men that they 

 have a consciousness like his own, so it may be inferred 

 from the behaviour of the frog that it possesses some 

 dim counterpart of the consciousness of mankind. An 

 unsolved and perhaps insoluble problem is presented by 

 the relation of consciousness to the events which it 

 accompanies. Is it caused by them ? Does it affect their 

 course? These are, of course, questions of the highest 

 importance to philosophy. All that need be said here is that, 

 though the consciousness of the living organism is probably 

 always accompanied with events in the nervous system, the 

 legitimate inference from 



a.c/t 



9- 



I. I. ■■■■ 



this is, not that either of cor. 



them is the cause of the 

 other, but rather that be- 

 tween them there is some 

 relation whose nature is un- 

 known to us. We are here 

 dealing with two things of 

 wholly different kinds, the 

 events which happen in the 

 nervous system being phy- 

 sical 1 processes and con- 

 sciousness a psychical pro- 

 cess. The difficulty in im- 



ncrinincr nnv intprarHnn «.«*., Anterior chamber; «*., choroid; «., 

 agining any interaction con j unct iva; cor., cornea; ir., iris; 



Is., lens ; /./., lower lid ; o.n. t optic 

 nerve ; p.ck., posterior chamber ; r. t 

 retina ; scl. t sclerotic ; u.l., upper lid. 



FlG. 1 41. — A diagram of a section 

 through the eye of a frog. 



between them lies in the 

 fact that such action would 

 apparently be contrary to 



the principle of the conservation of energy, though this has 

 been denied. On the other hand, it seems equally clear 

 that consciousness cannot be talked or written about, or, if 

 thinking be dependent upon processes in the brain, even 

 thought about, unless it affect the nervous system. 



The senses of a backboned animal, such as a frog, are more 

 numerous than is generally realised. Besides the "five 

 senses " of sight, hearing, smell, taste, and touch, there 

 are distinct kinds of sensibility to heat, cold, and the move- 

 ments of the body, and an indefinite " general sensibility " 



1 That is, processes which go on in material bodies ; not necessarily 

 " physical" in the sense in which that term is opposed to " chemical." 



