338 EDEMA 



surely go ou between the vessels aud the tissue-cells, and the condi- 

 tions which determine the water content of our colloid solutions 

 constantly vary. The question that remains is, do these two 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 Ij'mph flow? They are purely physical or mechan- 

 ical causes, and the "vitalist" school will claim that they are inade- ^ 

 quate 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 varying 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 lymph — a con- 

 siderable and perhaps the greater part of them is absorbed back 

 into the capillaries directly. A classical proof of this is the experi- 

 ment 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 prob- 

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

 wiiether substances are absorbed by the blood-vessels under normal 

 conditions. 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 

 absorption depended upon the "vital activity" of the cells. ^Fore 

 nearly reproducing normal conditions were the experiments of Star- 

 ling and Tubby, who found that -methylene-blue or indigo-carmine in- 

 jected into the pleura or peritoneum appeared in th(^ urine long be- 

 fore it colored the lymph in the thoracic duct.'** Adler and Meltzer 

 found evidence, however, that not all the absorption is accomplished 

 by the blood-vessels, for obstruction of the thoracic duct retards ab- 

 sorption. That the absorption is not dependent solely upon the cir- 

 culation and blood pressure is shown by the fact tiuit absorption 

 from the peritoneal cavity occurs in dead bodies (Hamburger, Adler 

 and Meltzer). 



The nature of the mechanism l)y wliidi Huids arc taken into tlie 

 blood-vessels is still unknown. We can easily understand tlie en- 

 trance of injected poisons and eoloring-mattei-s from the tissues into- 



isStHJ Mendel, Amer. Jour. Physiol., 1899 (2), 342. 



