6 
Mr. Home's Lecture 
The posterior half of a cat’s eye, while in a very recent state, 
was immersed in a bason of water, and examined. The tapetum 
appeared very bright, the retina not having acquired sufficient 
opacity to become visible : the entrance of the optic nerve was 
a very white spot, which seemed to be opaque; but, when 
small pieces of coloured paper were alternately placed between 
the outside of the eye and the bottom of the bason, their colour 
was distinctly seen in the cavity of the eye, through the sub- 
stance of the optic nerve ; so that, at this part, the internal 
structure of the nerve has a degree of transparency. 
This appeared to be a newly-discovered fact ; and, to ascer- 
tain whether it was really so, the works of several physiologi- 
cal writers were consulted, but nothing was found which gave 
an idea that their authors had the smallest knowledge of it. 
This semi-transparent state of the internal parts of the optic 
nerve, while recent, led naturally to the examination of its 
substance, by means of magnifying glasses; and, notwithstand- 
ing the failure of so many men of superior abilities, in this in- 
tricate inquiry, it held out the hope of meeting with some suc- 
cess. 
The principal theories which have been formed respecting 
the structure of nerves, have been taken notice of by Fontana : 
as they all differ from the observations which will be stated in 
the .present Paper, it may not be improper to mention the 
heads of each of them, so as to bring into one point of view, all 
the knowledge that has been acquired on the subject. 
Torre found the medullary substance of the brain, spinal 
marrow, and nerves, to be a mass of transparent globules, 
swimming in a transparent fluid. When the parts were mag- 
nified one thousand times, the globules appeared largest in the 
