THEORIES OF LUDWIG AND HEIDENHAIN. 



297 



Heidenhairis first class of lymphagogues. We are now in a position to 

 discuss the mode of action of the animal poisons included in the first 

 class of lymphagogues. On injecting a decoction of crayfish, leeches, or 

 mussels into the blood, the lymph flowing from the thoracic duct is 

 increased in amount, and becomes much more concentrated than before. 

 In 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 the 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 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 



Inj. of 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.) 



increased lymph flow observed after injection of lymphagosrues 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- 



