DEVELOPMENT OF LOBULE OF PIG’S LIVER 305 
ulum of the septum stained by the Bielsechowsky method and 
believe that a thickening of it at this stage is very doubtful. 
In a slightly longer pig measuring 265-mm. (also unborn) 
a somewhat similar condition is found, although it is not quite 
so far advanced as the 254-mm. specimen. This variation 
in the degree of development I have found to be especially 
marked in stages around birth. Thus, in specimens of two 
hours and twenty-four hours after birth, the septa appear no 
more distinct than those of the 265-mm. stage, while a speci- 
men of three days is no further advanced than a 254-mm. 
embryo. A similar varation in the degree of development is 
noted by Theopold (10). Again a radial arrangement of the 
hepatic cells is absent. 
In a pig of four days the liver shows a more advanced con- 
dition (fig. 4). The cells are coarsely granular and stain deeply. 
The lobules are in most places definitely marked out by the 
arrangement of their border cells. This consists in their form- 
ing continuous sheets of cells about each lobule; thus, when 
seen in cross-section, they form two parallel rows. Between 
these rows of cells is found reticulum which is slightly thick- 
ened, but contains no collagen fibrils. A Berlin-blue-gelatin 
injection of the liver of a second pig of four days also shows 
definite evidence of the lobular nature of the liver. As shown 
in figure 5, the injection mass has passed through the sinu- 
soids into the central veins. The sinusoids between the lobules, 
although present and forming free anastomoses between one 
lobule and another, are smaller and somewhat less numerous 
than those within the middle of the lobules. This condition 
results in the appearance shown in the figure, the lobules being 
separated from one another by a clear translucent zone—an 
appearance which is more strikingly brought out in the thick 
sections. 
For the first time can a radial arrangement of the liver cells 
be seen. This point is shown in the injected specimen, since 
the direction of the trabeculae of liver cells corresponds with 
the direction of the sinusoids. Although the radial arrange- 
ment is not well marked at this stage, it becomes increasingly 
