88 The Microscopic Structure Mn eae 
duct, into them. This, however, is not always the case, for there 
are many places met with, in which we find both sets of capillaries 
injected with their respective colours (Fig. 1). 
If a thin transparent section, in which both capillary networks 
are injected, be examined under the microscope, the two sets of capil- 
laries can be readily distinguished as they interlace with each other. 
In making such examinations, the sections should be illuminated 
from above and below; and for this purpose, a condensing lens of 
no less than three inches diameter should be used. After the mirror 
and condenser are properly adjusted, and the section thus illumi- 
nated by reflected and transmitted light, the attention of the ob- 
server should be directed to one particular spot of the section where 
both sets of capillaries are injected. By turning the mirror slowly, 
either reflected or transmitted light may be made to predominate, 
and the examination carried on very successfully. _ Examinations 
of such sections by oblique light are also of great importance. 
In comparing the interspaces of the network in a thin section, 
in which only one set of capillaries is injected with those of another 
section in which both sets are injected, they will be found larger in 
the former than in the latter; this shows that the networks inter- 
lace with each other. 
In very thin sections in which one set of capillaries is injected 
with the coloured material, and the other only with the uncoloured 
solution of Canada balsam, the walls of the uncoloured capillaries 
can be distinctly observed, as they accompany and cross the former, 
if examined with an objective of 4 or + of an inch focal length. 
The meshes of the network of “biliary tubules” are very regular, 
and the walls of the latter can be distinguished without difficulty. 
The regularity of the vessels of this network, when injected with 
Prussian blue, exceeds even that of the capillaries of the blood- 
vessels. I have seen the biliary tubules so well filled with Prussian 
blue, that they appeared almost black, but were still retaining the 
regular form of their meshes; this strongly serves to prove that 
they possess walls as strong as other capillaries. 
Sometimes, in examining thin sections, places are met with in 
which the biliary network is well injected and very regular, while 
the interspaces are slightly tinged with the colour—Prussian blue. 
At first sight this might be taken for an extravasation; but by 
closer examination, it will be found that this tinge is produced by a 
transudation of the injecting liquid—coloured by the exceedingly 
fine Prussian blue—from the biliary tubules into the hepatic cells. 
I have convinced myself of this fact, by putting small pieces of fresh 
liver into the blue injecting material, and by examining minute 
fragments of it after some hours had elapsed; in such cases I 
always found the blue colour in the interior of many of the cells. 
Another mode to study the network of biliary tubules is by 
