PEOPERTIES AND FORMATION OF LYMPH 239 



The influence which the capillary blood pressure possesses upon 

 the production of lymph, may be more fully portrayed in the follow- 

 ing manner. If the lymphatics of the liver are ligated, the largest 

 part of the lymph traversing the thoracic duct, must of course be de- 

 rived from the intestines. If the thoracic aorta is now obstructed, the 

 flow of lymph ceases, owing to the diminished capillary pressure. 

 Just the opposite effect, namely, a heightened driving force and an 

 increased discharge of lymph, may be obtained by obstructing the 

 portal vein. A similar experiment may be performed upon the liver 

 itself. If the inferior vena cava is compressed centrally to the orifice 

 of the hepatic vein, a pronounced diminution of the general blood 

 pressure results which, however, is accompanied by an increase in the 

 flow of the lymph from the thoracic duct. In view of the fact that the 

 obstruction of the vena cava leads to an engorgement of the blood- 

 vessels of the liver and a local rise in the capillary pressure, this result 

 cannot surprise us, and especially not if it is noted that the occlusion 

 of the hepatic vein remains without effect, provided that the lymphatics 

 of this organ have been ligated beforehand. An augmentation of the 

 capillary pressure of the posterior extremities may be produced in an 

 easy way by blocking the venous return, but, curiously enough, this 

 procedure does not materially increase the flow of lymph from this 

 particular part of the body. Starling endeavors to unify these data 

 by assuming that the height of the pressure plays a paramount role 

 in the formation of lymph only in those organs in which the capil- 

 laries are very permeable, while in those organs in which they are rela- 

 tively impermeable, other factors are brought into play. 



The view of Heidenhain is based upon a number of facts which, 

 however, do not deny that filtration plays a part but merely tend to 

 prove that this factor is not the only one concerned in the formation 

 of lymph. This author shows first of all that the different organs are 

 quite unable to derive their entire supply of inorganic and organic 

 material from lymph which is formed exclusively by filtration, because 

 a quantity of fluid would be required to satisfy their needs which would 

 be very much larger than that actually present in our body. For 

 example, as 1.7 grams of CaO are contained in 1.0 kg. of cow's milk, 

 the entire product for 24 hours would embrace about 42.5 grams of 

 this substance. In order to render this amount available to the secre- 

 tory cells of the mammary glands, 236 liters of lymph would be 

 required, because this substance is normally present in a concentra- 

 tion of only 0.018 per cent. This discrepancy can only be explained 

 by assuming that the filtration is associated with osmosis and diffusion 

 which processes would naturally tend to augment that production of 

 lymph which is had by pressure alone. 



Heidenhain has also called attention to the fact that the increases 

 in the flow of lymph are not always associated with rises in the capil- 

 lary blood pressure. In testing the influence which the exclusion of 

 different tissues and organs exerts upon the lymph flow, it was found 



