AND FUNCTION OF THE LIVER. 
23 
the ducts which present the structural characters that appear indicative of an active 
function, i. e. those which approach their termination, are in contact with paren- 
chymal cells and celloid particles containing varying quantities of sugar, albumen 
and oil ; they are also surrounded by the rather scanty plexus of the terminal twigs 
of the hepatic artery, and moreover they run in such close relation with the delicate 
walled portal vein branches that they may possibly receive plasma exuded from them. 
In fishes’ livers, where the quantity of fibrous tissue is small, it is very remarkable to 
observe how the ducts are encrusted with the oily parenchyma, as it were bathed in 
its fluid; in this instance it is impossible to avoid the idea that this abundant oil 
serves to the ducts as a plasma, out of which, by means of their epithelium, they elabo- 
rate bile. The same must hold in cases of fatty liver in higher animals ; and generally 
it seems probable that the parenchyma furnishes a suitable fluid (which may often 
be in part already of biliary nature) which the ultimate ducts employ in their 
eliminative action. 
Now have we any evidence tending to show that an active change is taking place 
in the ultimate ducts, — that they are more than mere efferent channels ? Such I think 
has been already detailed, and I will refer to it here again. 
The presence of abundant granulous matter in the ultimate ducts of fishes’ livers 
speaks in favour of an active change proceeding in these parts, as also do the pellucid 
vesicles, which often crowd together so closely in them ; such surely would not be 
found in a mere efferent canal. Compare the condition of the epithelium of the 
cortical renal tubuli of those in the medullary cones as an illustrative instance ; in the 
first, the nuclei, surrounded with abundant granulous matter, constitute celloid parti- 
cles and sometimes cells ; in the other, the nuclei lie applied against the limitary wail 
almost naked and alone. Manifestly the one is a secreting part, the other a mere 
channel of exit. In Reptiles and Birds the case is the same ; the ultimate ducts are 
not lined by small epithelial particles, but well nigh filled with vesicles or granulous 
matter, which must be supposed to be continually breaking up into the fluid secre- 
tion and some complementary matter. In Mammalia we meet ordinarily with a 
seemingly different condition of the ultimate ducts, which, though rare, also occurs 
in Fishes and Reptiles. The nuclei are not buried in granulous matter, but are set 
as it were in a thin layer of it, and leave a distinct central channel between the oppo- 
site walls ; yet they are not formed into distinct particles ; there are no columnar 
cells like those of the larger ducts; the nuclei abide in all their separate entireness. 
Have we knowledge of any secretory structure similar to this, with which we may 
compare it, and which may aid us to comprehend it better? Such a one is found in 
the cavities of the thyroid, where the epithelial layer, precisely similar in constitution 
to the walls of the ultimate biliary ducts, rests externally upon the limitary membrane, 
and internally is in contact with the secretion it has elaborated. Can we interpret 
the import of this arrangement? Can we perceive its peculiar significance? It seems 
scarcely doubtful that the more perfect a cell is the greater is its permanence ; a 
