209 
. “ The first two drawings are representations of what are received 
as longitudinal and transverse sections of common household coal, to 
which, for the present, I shall confine my remarks. 
“Professor Bennett expresses it as his opinion—and I believe he 
holds it in common with others — that the red coloured striz seen in 
the longitudinal section are tubes or ducts; that the yellow rings seen 
in the transverse section are the ends of those tubes; and that the red 
colour of the tubes, like blood seen in the veins of the frog’s foot, is 
an aggregation of the yellow bodies strewed over the section like 
blood-cells in single file. 
“ For a moment let us reflect upon the appearance presented by a 
cell or tube, as seen on the field of the microscope. In order that 
either of these bodies may be seen by transmitted light, a certain 
amount of transparency is necessary: the slightest curvature or undu- 
lation on the surface causes the light thrown from the reflector to be - 
diverted from the eye of the observer, and the part so curved appears 
dark ; this is invariably the case at the margins: the outlines of such 
bodies are distinctly defined and black, whatever may be their colour 
or form, and this blackness is diffused inwards according to their 
rotundity. 
“ How is it, then, that histologists have in this case departed from 
an invariable optical law, and have described appearances void of out- 
line as cells and tubes? But even admitting them to be so, I would 
then ask, why have these not been carbonised like the adjacent struc- 
tures which form the black mass? Wanting these two characteristics, 
no one need hesitate to say that they are neither cells nor tubes, 
“ With regard to the red colour being an aggregation of the yellow, 
it is enough simply to state that that is impossible, from two facts— 
the section is reduced to an equal thickness, and_ the yellow bodies 
occur within the red spaces, their definition being then as complete as 
when embedded in their usual black matrix. 
“T have said that Mr. Quekett expresses a notion similar to mine, 
but again returns to the usually received opinion; here are his 
words : —‘If a small cubical block of any kind of coal be examined 
under a power of fifty diameters, four of its six sides will exhibit. more 
less of a fibrous structure, precisely like that of wood.’ 
“ Now, if a block of wood and a block of coal be examined together, 
with the longitudinal strize of each laid in the horizontal direction, 
they will present very different appearances. In the case of the wood 
it will be seen that only two of its sides, which I shall call the back 
and front, present the striated appearance ; in the other two the ends 
VOL. V. 2E 
