ABSORPTION 409 



fluid is required to form the secretion. In other organs, however, 

 such as the muscles and the ductless glands, it is probable that 

 the augmented irrigation rendered necessary by functional 

 activity is always associated with an accelerated flow of lymph, 

 which carries off the surplus liquid, including a portion of the 

 waste products. It is possible that an important factor in the 

 production of oedema may be the derangement of the mechanism, 

 whatever it is, through which the adjustment of the rate 

 of formation of tissue liquid to that of lymphatic lymph is 

 achieved. But it must be remembered that in all the organs 

 the blood capillaries not only supply materials to the tissue spaces, 

 but take up materials from them. So that, while the lymphatics 

 constitute an important drainage system, the bloodvessels 

 irrigate the tissues and drain them as well. 



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. Further, after division or embolism of the medulla 

 oblongata, 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 con- 

 tinue even after death (Pugliese). The action of the first class 

 of lymphagogues, which cannot be explained as the conse- 

 quence 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, Starling- 

 attributes to an injurious effect on the capillary endothelium 

 (and especially on the endothelium of the capillaries of the liver, 

 since nearly the whole of the increased lymph-flow comes from 

 chat organ), which increases its permeability. But it is not easy 

 to distinguish an increase of permeability produced by lympha- 

 gogues from an increase of secretoiy 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 colloids is filtered through a thin membrane, 

 the percentage of crystalloids in the filtrate is never, at most, 

 greater than in the original liquid. And although Cohnstein 



