CHAP. I. OF THE ELEMENTARY ORGANS. 
3 
ill-constructed glasses, is now generally abandoned. The 
supposed pores, with their rim, have been ascertained to be, 
in many cases, nothing but grains of semi-transparent matter 
sticking to the membrane : this has been proved by Dutrochet, 
who found that boiling them in hot nitric acid rendered them 
opaque, and that dipping them in a solution of caustic potash 
restored their transparency, — a property incompatible with a 
perforation; and any one furnished with a good modern 
miscroscope may satisfy himself upon the point, without 
going through Dutrochet's process ; by simple movement in 
water the grains may be often detached. In other cases 
they may be thin spaces in the sides of tissue, such as might 
be produced by the adhesion and separation at regular inter- 
vals of a thread developed spirally within a membranous sac. 
Such a view has been taken of them by Slack [Trans, 
Soc. Arts, xlix.), as will be explained at page 16. A nearly 
similar opinion was previously offered by Mohl, who considers 
the dots on the membrane of tissue to be thinner portions of 
it. He says it may be distinctly seen by the aid of a power- 
ful microscope that the little round orbs which are visible in 
the surface of membranes in the tissue of Palm-trees are pas- 
sages (meatus) in the thickness of the membrane, opening 
into the cavity of the cells, and closed externally by the mem- 
brane itself. He adds, that when dotted tissue is in contact, 
these passages are placed exactly opposite to each other. (Mar- 
tins Palm, Anat, v. col, 2.) In matters demanding such very 
delicate observation as this, it is excessively difficult to know 
what dependence can be placed upon the statements and draw- 
ings of even the most skilful anatomists. We must therefore 
wait for further evidence of these supposed facts before they 
can be received into the certain truths of science. It, however, 
occasionally happens that holes do exist in the membrane, of 
which mention will be made hereafter. 
Elementary Fibre may be compared to hair of inconceivable 
fineness, its diameter often not exceeding the ts^^tt of an inch. 
It has frequently a greenish colour, but is more commonly trans- 
parent and colourless. It appears to be sometimes capable 
of extension with the same rapidity as the membrane among 
B 2 
