338 EDEMA 



view of the physical school that "secretion" and "attraction" by 

 the cells are merely the outcome of physical forces; the causes of 

 lymph formation then reduce themselves to absorption, filtration and 

 diffusion. There has been, until recently, no question but that lymph 

 does escape from the vessels through simple filtration, for the pressure 

 inside the capillaries is presumably greater than outside, the capillary 

 walls are not water-tight and they are not impermeable to the sub- 

 stances dissolved in the plasma.^" Likewise osmotic exchanges surely 

 go on between the vessels and the tissue-cells, and the conditions 

 which determine the water content of our colloid solutions constantly 

 vary. The question that remains is, do these few factors account for 

 all of the lymph formation, and are they sufficient by themselves to 

 explain the physiological regulation and the pathological variations 

 in the lymph flow? They are purely physical or mechanical causes, 

 and the "vitalist" school will claim that they are inadequate and 

 that "vital activities" of the cells play the deciding role. But at 

 present the evidence that is being accumulated seems to point more 

 and more strongly to the conclusion that these "vital activities" 

 are but the result of simple well-known physical forces acting under 

 very complex conditions — complex because of the large number of 

 different chemical compounds occurring together, and the varj^ing in- 

 fluence of circulation, food supplies, cell structure, etc. 



ABSORPTION OF LYMPH 



By no means all the fluid that escapes from the vessels, nor all the 

 products of cell metabolism, are carried away in the l3'mph — a con- 

 siderable and perhaps the greater part of them is absorbed back 

 into the capillaries directly. A classical proof of this is the experiment 

 of Magendie, who observed that if poisons were injected into the leg 

 of an animal, which had been separated from the body entirely except 

 for the blood-vessels, that poisoning developed in the usual manner. 

 In such experiments the lymph-vessels are severed and probably 

 largely occluded; hence it does not solve the question as to whether 

 substances are absorbed by the blood-vessels under normal condi- 

 tions. Orlow found, however, that during absorption of fluid from the 

 peritoneal cavity there is no perceptible increase in the lymph flow from 

 the thoracic duct. Addition of sodium fluoride, a protoplasmic poison, 

 was found to interfere with this absorption, for which and other reasons 

 Heidenhain and Orlow considered that the absorj:)tion doixMuled upon 

 the "vital activity" of the cells. More nearly reproducing normal 

 conditions were the experiments of Starling and Tubby, who found 



*° Hill ("Recent Advances in Physiology and Biochemistry," 190G, p. 618) dis- 

 putes the possibility of such a thing as filtration prcssiu'c, on the ground that 

 the structures within the capsule of an organ must all be under tlie influence 

 of the blood pressure alike; but with the presence of an outlet for the fluid, as 

 in glands with ducts, filtration pressure surely can apply. 



