SUPERIOR ANIMALS. 165 
appear in motion, and are of frequent occurrence 
in some diseases, such as typhus fever, when the 
invalid sees them upon the bed-cover, and con- 
stantly endeavours to pick them off with his 
fingers. When a blow is received upon the eye, 
an intense light is perceived : this must be familiar 
to pugilists. 
When the optic nerve 1s cut, no pain is felt ; but 
an intense flash of hight across the eyes is experi- 
enced. ‘The same flash occurs when an electric 
current passes through the optic nerve, as some- 
times happens when a piece of silver and a piece 
of zinc are made to form a galvanic couple with 
the tongue or other parts of the mouth. ‘To en 
sure the success of this experiment, the plates of 
zinc and silver should be placed upon the inside 
of each cheek, and connected together, outside 
the mouth, with a piece of silver wire. 
I have observed very vivid luminous appear- 
ances, during fever, im my own eyes; they mani- 
fested themselves after any violent exertion, such 
as going upstairs, walking quickly across a room, 
etc.* The hight appeared in the form of myriads 
of luminous spots, in rapid motion, and of a 
greenish-yellow tint. 
These phenomena, to which I have given the 
* These actions would not amount to violent in a state of 
health, but require a great amount of exertion during illness. 
