296 PRODUCTION 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 *ts 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 injury, such as that caused by plunging the limbs 

 into water at 56 C. for a few minutes. Cohnheim 1 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 lymph 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 Virclww's Archiv, 1877, Bd. Ixix. S. 516. 



2 Ibid., 1883, Bd. xciii. S. 259. 



