Franklin P. Mall - 275 
where all of the veins are of one order; the six central veins of the embryo 
become permanent main trunks in the adult. In development, the liver 
structure shifts distalwards, successively tearing off its capillary connec- 
tions with the main veins, gradually rearranging the architecture of the 
lobules, often fracturing them and scattering them. Portions of each of 
the six primary lobules go to thousands of new lobules. None of the 
main trunks of a large liver, like that pictured in Fig. 27, give off capil- 
laries at birth. So we must conclude that in a child the liver structure 
is entirely rearranged each year which calls for a destruction and regen- 
eration of at least a billion capillaries and towards puberty ten times this 
number. 
In the estimation of the number of blood-vessels of the liver it has 
been found convenient to classify the branches of the vascular tree under 
six orders, designating the main trunks as the first order and those di- 
rectly related to the lobule as the sixth order. It is seen by studying Fig. 
27, which is from an embryo of the eighth week, that but the first three 
orders are present with capillaries arising from all of them. By the 
time the liver is fully formed each of the third order, which are 700 in 
number, must give rise to an equal number of those of the sixth order, 
while the liver increases 7000 times in volume. It follows that the lobule 
must increase in volume as the liver grows, and, in fact, this is the case. 
When the lobules are well formed, as at the end of the second month, 
they are .5 mm. in diameter; at birth 1 mm., and in the adult 1.5 mm. 
Actual measurement also shows that the weight of the liver at the end 
of two months is .2 gms.; at birth, 75 gms. and in the adult 1500 gms. 
As the lobules are shifting more distalwards, it is found that the cap- 
illaries have a greater and greater tendency to arise from a single order, 
so that when the liver is fully formed capillaries arise only from the sixth 
order of the branches of the portal vein, and from the fifth and sixth 
orders of the hepatic vein. It is evident then that the stretching of the 
liver is in all directions and that there are additions to the tip of all of 
the blood-vessels, both within the liver and on the periphery. Not only 
is the liver tissue shifted more distalward, but the vessels already laid 
down are stretched, and from their trunks new vessels arise to supply 
new Jobules which have arisen from fractured portions of adjoining 
lobules. 
Toldt and Zuckerkandl“ have advanced ideas similar to the ones I have 
formulated above. They state that the younger the liver the simpler is 
its vascular system, and that in the youngest stage the whole liver may be 
31 Toldt and Zuckerkandl, Sitzungsber. d. K. Akad. d. Wiss., Bd. 72. Wien, 
1876. 
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