ABSORPTION OF LYMPH 339 



that mcthylonc-bluc or iiuligo-carniiii(> injected into the pleura or 

 peritoneum appeared in the urine long before it colored the lymph in 

 the thoracic duct.^^ Adler and Mcltzcr found evidence, however, 

 that not all the absorption is accomplished by the blood-vessels, for 

 obstruction of the thoracic duct retards absorption. That the ab- 

 sorption is not dependent solely upon the circulation and blood pres- 

 sure is shown by the fact that absorption from the peritoneal cavity 

 occurs in dead bodies (Hamburger, Adler and Meltzer). 



The nature of the mechanism by which fluids are taken into the 

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

 trance of injected poisons and coloring-matters from the tissues into 

 the blood, because they are more concentrated at the point of injection 

 than in the blood, hence they may diffuse directly through the capil- 

 lary wall. Likewise we can understand the diffusion of water from 

 a hypotonic solution into the blood, but how a solution of the same 

 concentration as that of the blood can enter the blood is difficult to ex- 

 plain. Cohnstein and also Starling attribute this absorption to the 

 proteins of the blood in the following manner: After a fluid is injected 

 into the tissues or serous cavities there occurs a diffusion exchange 

 between this fluid and the blood, until the concentration of the crystal- 

 loids in each is equal; but the proteins of the blood cannot diffuse, 

 and as they exert a positive although very slight osmotic pressure, 

 this difference in osmotic pressure in favor of the blood causes diffu- 

 sion of the extravascular fluid into the blood. Roth has also applied 

 this idea in a rather comphcated manner to the absorption occurring 

 in metabolic processes (see Meltzer), but it must be admitted that it is 

 an unsatisfactory solution of the problem. Fischer would ascribe the 

 passage of fluid to the relative affinity of the colloids of the blood and 

 of the tissues for the fluid, and this would be towards the blood when- 

 ever the blood colloids had, from whatever possible cause, a greater 

 affinity for the fluid than the tissue colloids. 



Passage of the fluid from the tissues into the lymph stream was very 

 easy to understand in the light of the older conception of the lym- 

 phatic circulation, namely, that the lymph-vessels were merely con- 

 tinuations of the interstitial spaces; we could then assume that as 

 soon as the fluid left the blood-vessels it was practically within the 

 lymphatic system, and was crowded along the lymphatic channels by 

 the vis a tergo, aided by the valves of the lymph-vessels and the intra- 

 thoracic vacuum. But it now seems, particularly through the studies 

 of MacCallum,22 that the lymphatic vessels form a closed system, not 

 in communication with the interstitial spaces. This being the case, 

 we have to explain the passage of the lymph through the walls of 

 the lymphatic vessels, and this is a problem which is not by any means 

 a simple one, and which has yet to be investigated. It is significant 



21 See Mendel, Amer. Jour. Physiol., 1899 (2), 342. 

 " Johns Hopkins Hosp. Bull., 1903 (14), 105. 



