47 FORMATION OF LYMPH 



of changes in the mechanical conditions of the blood and lymph 

 circulations, alterations in the tissues must be recognized as among 

 the causes of oedema (Fischer). Thus it is clear that the interpre- 

 tation of such an apparently simple experiment as the production 

 of oedema by the ligation of a vein needs great care. Whatever it 

 proves, it may be said with confidence that it does not prove that 

 the increased capillary pressure is the direct cause of the oedema. 



A mere increase in the capillary blood-pressure does not of itself 

 accelerate the formation of tissue liquid from the blood any more 

 than that of lymph from the tissue liquid, as is shown by the fact 

 that, when the chorda tympani is stimulated after injection of a 

 dose of atropine sufficient to prevent all salivary secretion, there is 

 neither oedema of the gland nor increase in the flow of lymph from 

 it, although the arterioles are as widely dilated as before. When the 

 blood-pressure is greatly increased in the anterior portion of an 

 animal by clamping the aorta, or in the whole animal by continued 

 stimulation of the cut medulla oblongata or the splanchnic nerves, 

 the blood does not alter in concentration in the least, showing that 

 no sensible increase in the passage of water into the lymph has 

 occurred. After division or embolism of the medulla oblon- 

 gata, and consequent paralysis of the vaso-motor centre and 

 general vascular dilatation, it is stated that the injection of sodium 

 chloride produces an increase in the lymph-flow as great and as 

 durable as in the normal animal, and which can continue even after 

 death (Pugliese). The action of the first class of lymphagogues, 

 which cannot be explained as the consequence of an increase of 

 capillary pressure, because the pressure in the capillaries is not 

 consistently increased, and may even in the case of some of these 

 lymphagogues be diminished, is attributed by Starling to an injurious 

 effect on the capillary endothelium (and especially on the endo- 

 thelium of the capillaries of the liver, since nearly the whole of the 

 increased lymph-flow comes from that organ), which increases its 

 permeability. But it is not easy to distinguish an increase of per- 

 meability produced by lymphagogues from an increase of secretory 

 activity of the endothelial cells. 



Hamburger, too, has brought forward results which it is difficult 

 to reconcile with a theory of filtration even for the second class of 

 lymphagogues. Further, Heidenhain has shown that some time 

 after injection of a crystalloid substance, like sugar, into the blood, 

 a greater percentage of the substance may be found in the lymph 

 than in the blood. Now, when a mixture of crystalloids and col- 

 loids is filtered through a thin membrane, the percentage of crystal- 

 loids in the filtrate is never, at most, greater than in the original 

 liquid. And although Cohnstein states that, if time enough be 

 allowed, the maximum concentration of sodium chloride in the 

 lymph, after intravenous injection, becomes approximately the 



