296 PROD UCTION AND ABSORPTION OF L YMPH. 
of secretory activity. We may conclude, therefore, that the increased 
flow of lymph caused by injection of the second class of lymphagogues 
is entirely due to the rise of capillary pressure thereby induced, and is in 
no wise conditioned by a stimulation of the secretory activities of the 
endothelial cells. 
The permeability of the capillary wall. — The dependence of lymph 
formation on capillary pressure is not the only important relationship 
brought to light by these experiments. The amount and composition of 
the transudation through a membrane depend not only on the pressure 
at which the transudation is effected, but also on the nature of the mem- 
brane. According to the permeability of the membrane, so the amount 
and composition in proteids of the transuding fluid will vary. After 
obstruction of the inferior vena cava, the pressure in the intestinal capil- 
laries, although it probably sinks below its normal height, is yet as high 
as that in the hepatic capillaries. Nevertheless, we get a very small 
amount of transudation through the intestinal capillaries, and a very large 
amount through the hepatic capillaries. Hence the permeability of the 
liver capillaries must be very much more marked than that of the intestinal 
capillaries. In the same way we may compare the permeability of the 
intestinal capillaries with those of the limb capillaries. Normally from 
the limb there is no flow of lymph at all, whereas a probably equal 
pressure in the intestinal capillaries suffices to give rise to a steady flow 
of lymph. If we ligature all the veins of the leg, a lymph flow may be 
set up, but such a flow is incomparably smaller than that produced on 
ligature of the portal vein. We can therefore arrange the capillaries of 
the body in a descending order of permeability, the liver capillaries being 
the most permeable and the limb capillaries the least permeable. I have 
already mentioned how, on filtering solutions of proteid through various 
membranes, the percentage of proteids in the filtrate increases with the 
permeability of the membrane. As we have seen, exactly the same 
thing holds good for the capillaries in the body. The lymph in the 
limbs, the filtrate through the impermeable limb capillaries, contains 
only from 2 to 3 per cent, proteids ; that from the intestines contains 
from 4 to 6 per cent, proteids ; while that from the permeable capillaries 
of the liver contains from 6 to 8 per cent, proteids — in fact, almost as 
much as the blood plasma itself. It is conceivable that we might alter 
the amount of lymph in any organ by changing, not the intracapillary pres- 
sure, but the filtering membrane, i.e. the endothelial wall of the capillaries. 
Such a change can be brought about in the body by various means. 
Thus the permeability of the limb capillaries is considerably increased as 
the effect of any local injur)-, such as that caused by plunging the limbs 
into water at 56 C. for a few minutes. Cohnheim x pointed out that if a 
cannula be placed in one of the lymphatics of the foot, and the foot be 
then scalded in this manner, in a few minutes the lymph begins to flow 
spontaneously from the cannula. The lymph which is thus produced is 
much richer in proteids than is lyniph from a normal limb. Moreover, 
as Jankowski 2 showed, the amount of lymph flowing from the foot can 
now be varied within wide limits by altering the pressure in the capil- 
laries, either by ligature of the vein or artery, injection of salt solution, 
or production of vasomotor paralysis. By this scalding, in fact, we may 
reduce the limb capillaries to the condition of liver capillaries. 
1 Virehow's Archir, 1S77, Bd. lxix. S. 516. 
- Ibid., 18S3, Bd. xciii. S. 259. 
