308 FRANKLIN PARADISE JOHNSON 
in situ, I have not determined. This point, it seems to me, is 
of little moment, inasmuch as in either case the origin is from the 
connective tissue of the portal canals. It is interesting to note 
that the connective tissue surrounding the sublobular veins 
does not take part in the formation of the septa to nearly so 
great an extent as does that of the portal canals. Around 
some of the larger sublobular veins a few out-pushing collagen 
fibrils may be found, but it is evident that the bulk of the con- 
nective tissue forming the septa springs from the portal canals. 
Capsula fibrosa (Glissoni). Collagen fibrils are differentiated 
in the pig’s liver as early as the 80-mm. stage. They are found 
principally in the portal canals, and to a less extent around the 
larger sublobular veins, being especially abundant in the region 
of the porta hepatis. Extending out in either direction from 
this region, as seen in the cross-section, there are thin strands 
of collagen fibrils which spread around, but do not entirely 
encircle the liver. These strands represent the forming external 
capsule of Glisson. A similar section of the liver of a pig 111 
mm. in length, shows a complete capsule. It consists, however, 
of a very delicate layer of collagen fibrils which lies close to the 
liver parenchyma. In all stages up to birth the capsule has 
this appearance, the collagen fibrils showing no appreciable 
thickening; on the other hand, in certain stages it appears to 
be less distinct than in the younger ones; in some its presence 
as a distinct layer is extremely doubtful. After birth it rapidly 
becomes thicker and continues to augment in strength and den- 
sity until the adult condition is reached. 
FORMATION OF NEW LOBULES 
Mall (’06), in his study of the structural unit of the liver, 
concluded that Thoma’s laws concerning the formation of new 
blood-vessels explain the formation of new lobules. He states: 
As the vessels grow the liver tissue increases In quantity, but the 
liver lobules do not increase in size indefinitely, because Thoma’s 
first law is constantly at work and will soon break up the larger lobules 
into a number of smaller ones. In all cases the length of the capil- 
laries remains constant, and when they appear to be too long and too 
