28 
Sir Everard Home on the 
quantity, or forms irregular flakes or splotches upon the 
glass, perfectly transparent, and of a yellowish tinge, as re- 
presented in PI. II. fig. 2. 
If a portion is cut off' from the brain in a fresh state, before 
it has been put in water, and laid upon a dry glass plate, and 
covered by a cup, so as to prevent evaporation, a perfectly 
colourless aqueous fluid is exuded, which evaporates on ex- 
posure to the air, and hardly leaves any mark upon the glass. 
The cortical substance of the cerebrum contains also a 
fluid resembling the serum of the blood ; it has a yellower 
tint than the fluids in the medullary substance, or any other 
part of the brain ; and, when dry, it assumes the glassy ap- 
pearance, and forms the same cracks that the serum does 
when dried on glass. 
The above are all the visible materials that can be distin- 
guished in the different parts of the human brain by means 
of the microscope ; and, making allowance for slight modifi- 
cations, are the same in different parts of the organ. 
The globules are from to 4^0 of an inch in diame- 
ter ; but the general or predominant size is T 2 I OQ . They 
are semi-transparent, and of a white colour, arranged into 
fibres of single globules, and seem to be held together by 
the viscid mucus. The fibres form bundles connected in the 
same way: 
The principal difference in the appearance of the different 
parts of the brain, consists in the proportions the quantity of 
mucus and fluids bear to the quantity of globular tissue 
in the same part, and in some respects in the size of the glo- 
bules ; as for instance, the cortical substance of the cerebrum 
and cerebellum, (which are in all respects alike) consists 
