C 25 3 
V. The Croonian Lecture. Microscopical observations on the 
following subjects. On the Brain and Nerves ; showing that 
the materials of which they are composed exist in the blood. On 
the discovery of valves in the branches of the vas breve , lying be - 
tween the villous and muscular coats of the stomach. On the stnic- 
ture of the Spleen. By aSu'Everard Home, Bart. V. P. R. S. 
Read December 7th, 1820. 
The Croonian Lectures for the three preceding years, con- 
tain Mr. Bauer’s microscopical observations on the blood. 
That fluid we find is made up of a greater number of ingredi- 
ents than it was known to contain ; indeed we find in it mate- 
rials ready prepared, for the formation of most of the struc- 
tures of an animal body. 
In the present Lecture, the brain and nerves form the first 
subject of investigation. Having found upon a former occa- 
sion that the retina is perfectly transparent in the living body, 
and is only rendered visible by coagulation after death, this, 
the only expansion of medullary substance in the body with 
which I am acquainted, was examined by Mr. Bauer in the 
microscope. 
He found the optic nerve to consist of many bundles of 
extremely delicate fibres, formed of minute globules con- 
nected together by a gelatinous substance, which readily 
dissolves in water. The dimensions of the globules, mea- 
sured on the micrometer, explained in the preceding Lectures, 
are from t0 40W P arts of an inch, mixed with very few 
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