3 o6 PROD UCTION AND ABSORPTION OF L YMPH. 
From a consideration of these facts we must conclude that lymph 
and saline solutions, isotonic with the blood, may he taken up by the 
blood circulating through the capillaries, and that this process may 
occur comparatively rapidly. 
Effect of intracapillary pressure. — We have already seen how 
any excess of intracapillary pressure, such as accompanies plethora, 
causes an increased transudation from the capillaries, so that the 
volume of circulating fluid is diminished. Now we see that, on any 
diminution of capillary pressure taking place, as after bleeding, the 
fluid in the tissue spaces goes back into the vessels to makeup for 
the volume of circulating fluid lost. This wonderful balance between 
capillary pressure and lymph production or absorption is, I think, 
well illustrated by Lazarus Barlow's observations. This author has 
shown that the slight plethora produced by wrapping up a limb in 
Esmarch's bandage causes an appreciable increase in the transudation in 
other parts of the body, so that the specific gravity of the tissues of the 
upper limb for instance falls, while the specific gravity of the blood 
rises. The reverse is the case when circulation is restored to a limb 
which has been kept anaemic for an hour or two. Here considerable 
hyperaemia of the affected limb is produced, and corresponding anaemia of 
other parts of the body. We find, then, that absorption as well as trans- 
udation through the capillary wall is determined by the intracapillary 
pressure. Y/hen the pressure rises transudation is increased, when the 
pressure falls absorption is increased. We have seen that the depend- 
ence of transudation on capillary pressure is susceptible of a fairly simple 
mechanical explanation. We have now to discuss the mechanism of the 
absorption process. 
Mechanism of absorption.— Filtration.— Is absorption effected by 
the active intervention of the endothelial cells, or are there physical 
factors at work which will serve to explain it ? An explanation of 
absorption, which will strike anyone who investigates this problem, is 
that it may take place in the same manner as lymph is produced, 
i.e. by a process analogous to filtration. A series of mechanical 
experiments by Klemensiewicz 1 would seem at first sight to show 
that such a backward filtration is impossible. Klemensiewicz points 
out that, if fluid be passing at a given pressure through a permeable 
tube contained within a rigid tube, transudation will occur until the 
pressure of the transuded fluid is equal to that of the fluid flowing 
through. At a certain point in the experiment the pressure of the 
transuded fluid will exceed the pressure at the outflow end of the 
tube. The tube will collapse and the flow through it will be stopped. 
He imagines that the same sequence of events occurs in the living 
body in the presence of a considerable transudation. Arteries, capil- 
laries, and veins are bathed in the transuded fluid. The fluid which 
leaves the capillaries will, if a free outflow for it be absent, after 
a time attain a pressure near that ruling in the capillaries and higher 
than the venous pressure. The veins will therefore collapse, venous 
obstruction will be produced, and the capillary pressure and trans- 
udation will be higher than ever, so that we have a vicious circle 
of events tending continually to increase the oedema of that part. 
Now Klemensiewicz' objections are true only under one condition — i.e. 
that the venous tubes should run freely through the lymphatic spaces of 
1 Sit-ungsb. <?. k. Akad. d. Wissensch., Wien, 1881, Bd. lxxxiv. ; 1886, Bd. xciv. 
