222 PHYSIOLOGY. 



51. There is a striking proof of design in the manner in 

 which the opaque, lining membrane of the eye-lids becomes 

 transparent, as it is reflected over the cornea. But we can 

 illustrate this more clearly by means of the following dia- 

 gram. 



Fig. 24. 



The eye-lids viewed from before ; a, a, the lachrymal canals ; J, the 

 iarchrymal sack. The lachrymal sack is a bag of an oval shape, fixed 

 to the end of the double canal, and lies in a depression of the nasal 

 bones. It terminates in a tube called the duct, which passes through 

 a hole made for it, in the bones of the nose, and opens into the nos. 

 tril. 



52. It is now well ascertained that a belief in superna- 

 tural appearances, and stories in relation to seeing ghosts, 

 hobgoblins, and spectres, have arisen from optical illusion. 

 We have seen how a person in delirium tremens, imagines 

 that he sees a thousand unreal objects, and hears a thousand 

 strange voices ; the same phenomenon, though less in degree, 

 may happen to a person in health, owing to an excitement 

 in some portion of the brain. I have heard an aged rela- 

 tive, who believed in witchcraft, tell of frequently having 

 seen the ghost of some deceased friend, and once of having 

 fired at a deer three times, in the twilight, while he was 

 cropping the tender grain just springing out of a newly 



