THEORIES OF LUDWIG AND I1EIDENHAIN. 
297 
HeidciiluTnt'sjirst class of lym/phagogues. — We are now in a position to 
discuss the mode of action of the animal poisons included in the first 
class of lyinphagogues. ( )n injecting a decoction of crayfish, leeches, or 
mussels into the blood, the lymph ilowing from the thoracic duct is 
increased in amount, and becomes much more concentrated than before. 
hi both blood and lymph coagulability is lessened or abolished; the 
blood becomes more concentrated from a loss of plasma, while the 
plasma itself is less concentrated than before the injection. The blood 
pressure, though generally lowered, may be unaltered if the injection be 
carefully carried out ; the heart-beat is always quickened. Heidenhain 
concludes that these bodies exert a specific influence on the endothelial 
cells, causing them to secrete an increased amount of lymph more con- 
centrated than the blood plasma. 
There can be no doubt that the greater concentration of the lymph 
obtained under these circumstances is due to th€ fact that it is chiefly 
derived from the liver, since the effect of these lymphagogues on the 
lymph flow may be almost abolished, if the portal lymphatics be liga- 
tured previous to the injection. On investigating the changes in 
capillary pressure consequent on the injection, I have found that they 
are not sufficient to account for the increased lymph production. It is 
true that injection of one of these bodies is invariably followed by a con- 
siderable rise of pressure in the portal vein, associated with general 
vascular dilatation. But this rise of pressure is comparatively transitory 
(Fig. 43), lasting only fifteen to forty minutes, whereas the increased lymph 
flow T lasts from forty 
minutes to two 
hours after the in- 
jection. Moreover, 
this rise of pressure 
in the portal vein 
would have more 
influence in in- 
creasing the capil- 
lary pressure in the 
intestines than in 
the liver. Taking 
these facts into con- 
sideration, we must 
conclude that the 
increased lymph flow observed after injection of lymphagogues of the 
first class cannot be accounted for by a rise of capillary pressure. It 
is open to us to conclude that these bodies act in Heidenhain's sense 
on the endothelial cells of the capillaries, exciting them to an active 
secretion. It must be remembered, however, that all these bodies are 
active poisons. We should expect them, therefore, to diminish rather 
than to excite the physiological activity of the endothelial cells. We 
have already seen that the effect of a slight injury to or diminished 
nutrition of the capillary wall is to increase its permeability. I would 
explain the action of these bodies, therefore, as dependent on injury to 
the capillary wall, and a consequent enhanced permeability, so that a 
pressure which is very little above the normal capillary pressure is able 
to cause a greatly increased transudation of fluid. 
I have already mentioned that these bodies chiefly affect the capil- 
O 34 7 10 
Inj. cf mussel extract 
Fig. 43. — To show effects of the injection of a lymphagogue of 
the first class on the blood pressures in the abdominal 
organs, and also on the lymph flow. (For explanation of 
curves see Fig. 41.) 
