/ HE R IES OF LUDWIG A A D HEIDENHAIN. 2 9 1 
hind-limbs we know that, in an animal at rust, on the tal.de, there is no 
lymph flow at all Hence the sources of the lymph arc confined to the 
trunk. We can, moreover, exclude the thorax and its contents, since 
ligature of the thoracic duct just above the diaphragm absolutely stops 
the lymph flow. Therefore, when dealing with the lymph flow from the 
thoracic duct, we deal only with the lymph coming from the abdominal 
viscera. As I shall show presently, the abdominal viscera, so far as their 
lymph is concerned, may be divided into two groups — (1) the viscera 
drained by the portal vein, and (2) the liver. 
Influence of venous obstruction. — In testing the filtration hypothesis 
on the lymph flow, we have to investigate whether the flow is always 
proportional to the difference between the intra- and extracapillary 
pressures. We may regard the extracapillary pressure as not varying 
to any large extent, so that we have to see what effect is produced 
on the lymph by variations in the intracapillary pressure in the 
intestines and the liver. The simplest experiments on the subject 
are those in which some large vessel is obstructed. Speaking generally, 
we may say that obstruction of a large vein raises the pressure in 
the capillaries immediately behind it, whereas obstruction of an 
artery will diminish the pressure immediately in front of it. If, 
for instance, we ligature the portal vein, the arterial pressure is very 
little affected, while the pressure in the vein behind the ligature 
rises enormously. In consequence of this, there is a large rise of 
pressure in the capillaries of the intestines and spleen, so that the 
spleen swells ami the intestines become black from venous congestion, 
haemorrhages being produced into their mucous membrane. The effect 
of this ligature on the lymph flow from the thoracic duct is to increase 
it four or five times. The lymph also becomes bloody and its total 
solids are diminished. The diminution in solids is clue solely to a 
diminution in proteids, the salts remaining the same as before ; so that 
we have here an increased capillary pressure, causing an increased trans- 
udation of lymph containing a diminished percentage of proteid — a result 
which is also obtained when proteids are filtered with pressure through 
dead animal membranes. The presence of red blood corpuscles in the 
lymph is not a necessary consequence of a rise of pressure in the 
portal vein. If a less excessive rise of pressure be produced by 
ligaturing the vein, not at its entry into the liver but just below the 
pancreatico-duodenal vein, thus leaving a circuitous mute for the blood 
to the liver through the anastomoses of this branch, an increased flow 
of lymph is produced, containing less proteids than normal lymph, 
but which may be quite free from red blood corpuscles. 
Still more striking is the effect produced by Heidenhain's experi- 
ment of obstructing the vena cava just above the diaphragm (i.e. 
between the opening of the hepatic veins and the heart). The lymph 
is increased from ten t" twenty fold, and it is found that the lymph 
obtained after the obstruction is free from red blood corpuscles ami is 
more concentrated than normal lymph. Thus, in one experiment of 
this description, the lymph flow rose from 3 c.c. in the ten minutes 
preceding the obstruction to 25 c.c. in the ten minutes after the vein was 
occluded. At the same time the percentage of sobds in the lymph rose 
from 4 - 8 per cent, before, to 6"6 per cent, after the obstruction. 
What is the cause of this increased lymph flow and why is it more 
concentrated \ To answer these questions we must find out first, the 
