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partial or total blindness might result, though the eyes 
themselves might remain intact. The special function of 
the eye was twofold: first, to bring the rays of light 
from external objects to a focus on the retina, so that an 
image is formed there as on the photographic plate of a 
camera ; second, to transfer the rays of light so focussed 
into nervous impulses, which are conveyed to the brain 
by means of the optic nerve. He then went on to ex- 
plain the formation of images by means of the cornea, 
the crystalline lens and the aqueous and vitreous humours.. 
The fact that these images are inverted, puzzles some 
people, who cannot understand how it is that we do not 
see everything upside down. This difficulty vanished 
when we realised that it is in the brain rather than in the 
eye that the power of vision resides. The functions of 
the iris were then described. Besides its importance 
from the esthetic point of view, it was useful for in- 
creasing the accuracy with which near objects are 
focussed, and it protected the retina from too much light. 
The way in which the eye could be adapted at one time 
for near and at another for distant vision was then ex- 
plained, the parts of the eye concerned being the 
crystalline lens with its suspensory ligament and the 
ciliary muscle. In youth the crystalline lens resembled 
a jelly enclosed in a bag, so that its shape could be 
readily altered by changes in pressure. But all through 
life it was becoming less like a jelly and more like a 
piece of glass, so that in middle life most people were 
obliged to have recourse to spectacles for near vision. 
Dr. Thompson next described the functions of the 
choroid and retina. The choroid coat being red, and 
the first non-transparent structure that was met with in 
looking through the pupil, the pupil itself would look red 
if sufficient light were thrown into it. The reason why, 
ordinarily, the pupil looked black was that the observer, 
