296 A Study of the Structural Unit of the Liver 
gelatin into any of the blood-vessels of the liver. I have usually found 
it most convenient to inject the gelatin into the portal vein, but it is just 
as easy to fill the lymphatics by injecting either the hepatic artery or 
hepatic vein. In all cases the colored fluid reaches the main lymph chan- 
nels in the same way. The colored gelatin flows with great ease from the 
capillaries at the center of the portal units as well as from those around 
the smaller hepatic veins into the lymphatics. After the lymphatics have 
all been filled it is well to inject a small quantity of fluid of different 
color into the blood-vessels. A much better method of making double 
injections is to mix red granules with a glue gelatin or blue granules with 
ase 
Fig. 54. Section through the center of a portal unit of a cat. X 500. 
Stained by Van Gieson’s method. The hepatic artery was injected with 
cinnabar gelatin, and the portal vein with Prussian-blue gelatin. L, lobule 
of liver; c, capillaries; a, artery; 1, lymph vessel; plv, persivacular lymph Jue 
space; pll, perilobular lymph space; w, bundles of white fibrous tissue be/ 
tween which are loose connective tissue fibrils and cells. 
a red gelatin, the fenestrated lining membrane of the capillary acting as 
a sieve which allows the fluid to pass but holds back the granules, as is 
the case with the blood corpuscles and plasma in life. 
When the portal vein is injected with Prussian-blue gelatin at a low 
pressure, it is found that in a few minutes the lymphatics are all filled 
with the blue mass. Livers injected in this way are best hardened in 
formalin and then cut by the freezing method, for alcohol causes the 
Ce 
