2 9 2 PROD UCTION AND ABSORPTION OF L YMPH. 
source of the lymph, and secondly, the condition of the capillary 
pressure in the organ or organs from which the lymph is derived. We 
can determine the source of the lymph by a process of exclusion. 
Tying the kidney vessels and lymphatics has no effect on the usual 
consequences of obstructing the inferior vena cava. On the other 
hand, if we ligature the lymphatics in the portal fissure which carry 
off the liver lymph, we find that a subsequent obstruction has no effect 
on the lymph flow, or indeed, may slightly diminish it. We must 
conclude that the excess of lymph production consequent upon the 
obstruction is entirely derived from the liver, and not, as Heidenhain 
thought, from the intestines. The change in concentration is easily ex- 
plained if we assume that, just as intestinal lymph is more concentrated 
(i.e. richer in proteids) than the lymph from the limbs, so the liver 
lymph is more concentrated than intestinal lymph, or than the mixed 
lymph obtained from the thoracic duct. 
In order to answer the question as to the cause of this increased 
production of lymph in the liver, we must investigate the changes in 
the circulation brought about by the obstruction. On obstructing the 
inferior vena cava and recording the blood pressure in the chief vessels 
of the abdomen, we notice that the pressure in the aorta drops almost 
at once to a third of its previous height, whereas there is a very 
considerable rise of pressure both in the portal vein and inferior cava. 
It is probable that the effect of the rise of portal pressure on the 
intestinal capillaries is more than counterbalanced by the severe drop 
in arterial pressure, so that there is a fall of pressure in the intestinal 
capillaries. This conclusion is borne out by the fact that, if the 
abdomen be open, the obstruction of the inferior vena cava is seen to be 
at once followed by blanching of the intestines, as Heidenhain pointed 
out. On the other hand, the effect of the simultaneous rise of pressures 
in the portal vein and vena cava must be to increase the pressure in 
the capillaries of the liver to three or four times the normal amount. 
We have then, as the results of this experiment, no rise of pressure in 
the portal area and no increase of lymph flow from the portal area, a 
large rise of pressure in the hepatic capillaries and a very large 
increase of lymph flow from the liver. 
Influence of aortic obstruction. — Another experiment, on which 
much stress has been laid by Heidenhain, is the one in which 
the descending aorta is obstructed in the thorax. The obstruction 
of this vessel is easily effected by passing an indiarubber balloon, 
tied on the end of a catheter, down the right carotid artery into 
the aorta just beyond the arch. The results of this obstruction on 
the lymph flow are somewhat variable. In most cases the lymph is 
diminished to one-half or one-third its previous amount; in a few 
cases the lymph is unaltered in quantity or even slightly increased. 
In all experiments the amount of proteids in the lymph is increased. 
Now, if we investigate the state of the circulation under these con- 
ditions, we find that obstruction of the thoracic aorta causes a very 
considerable fall of pressure in the aorta below the obstruction and 
a corresponding fall in the portal vein, whereas the pressure in the 
inferior vena cava is unaltered or in some cases even slightly increased. 
We must conclude, therefore, that in the intestinal capillaries the 
pressure has fallen considerably below its normal limits, while in the 
hepatic capillaries the pressure is very little altered or may even be 
