4 
Mr. Home’s Lecture 
iris ; a part of the light reflected from the tapetum being 
thrown back, by the concave surface of the cornea, upon the 
anterior surface of the iris, giving it a bright shining ap- 
pearance. 
The influence which the will of the animal has over this lu- 
minous appearance, seems altogether to depend on the con- 
traction and relaxation of the iris. When the animal is 
alarmed or first disturbed, it naturally dilates the pupil, and 
the eye glares ; when it is appeased or composed, the pupil con- 
tracts, and the light in the eye is no longer seen. 
The most material information that has been gained in this 
investigation, is the transparent state of the retina in the eye 
during life ; the opaque membranous appearance which it puts 
on in the dead body not being natural to it, but a change which 
takes place in consequence of death. This fact is almost all 
that is necessary, to explain the luminous appearance in the 
eyes of cats. 
That neither Baron Haller nor Fontana had an adequate 
idea of the transparency of the retina, will appear from the 
following expressions respecting it, taken from their works : 
Haller describes it in the following words, 
“ Membranam crassam quidem, sed mollisimam, pellucidam 
“ utique, quando recens oculus inspicitur, ut per earn sub aquis 
“ choroideam videas; tamen ex flavo subcineream.”* So that, 
although he calls it transparent, he says it is of a yellowish 
ash-colour. 
Fontana’s expressions are, “Cette insensibility de la ratine 
“ a la lumiere, en tant que lumiere, dyrive-t-elle de ce que les 
“ nerfs sont encore trop gros, et ne sont pas bien dycouverts des 
* Elementa Physiologies, Tom. V. p. 385. 
