LYMPH AND LYMPHATIC GLANDS. [CH. xxn. 



fluids subjected to experiment, have an important influence, as might be 

 anticipated, on the rapidity and duration of the osmotic current. Thus, if a 

 piece of ordinary bladder be used as a septum between water and alcohol, 

 the current is almost solely from the water to the alcohol, on account of the 

 much greater affinity of water for this kind of membrane ; while, on the 

 other hand, in the case of a membrane of caoutchouc, the alcohol, from its 

 greater affinity for this substance, would pass freely into the water. 



The general question of osmosis will be more fully discussed in relation to 

 the work of the kidney. 



If the lymph is produced by a simple act of filtration, then the 

 amount of lymph must rise and sink with the value of D d ; 

 D representing the capillary blood-pressure, and d 

 the pressure in the tissue spaces. 



In support of this mechanical theory, various 

 workers in Ludwig's laboratory showed that in- 

 creased capillary pressure due to obstruction of 

 the venous outflow increases the amount of lymph 

 formed ; and that diminution of the pressure in 

 the lymph spaces, by squeezing out the lymph 

 previously contained in them, leads to an increase 

 in the transudation. 



On the other hand, there were some facts which 

 could not be well explained by the filtration theory, 

 among which may be mentioned the action of curare 

 in causing an increase of lymph flow. 



Heidenhain was the first to fully recognise that 

 the laws of filtration and osmosis as applied to 

 dead membranes may be considerably modified 

 when the membranes are composed of living cells ; 

 and he considered that the formation of lymph is 

 due to the selective or secretory activity of the 

 endothelial walls of the capillaries. This so-called 

 vital action of the endothelial cells is seen in the fact that after 

 the injection of sugar into the blood, in a short time the 

 percentage of sugar in the lymph becomes higher than that in the 

 blood. There must, therefore, be some activity of the endothelial 

 cells in picking out the sugar from the blood and passing it on to 

 the lymph. 



Heidenhain is also the inventor of the term lymphagogues 

 (literally lymph drivers). These are substances like curare, which 

 have a specific action in causing an increased lymph flow. 

 Heidenhain considers the majority of these act by stimulating the 

 endothelial cells to activity. This conclusion, however, has been 

 subjected to much criticism. In this country the question has 

 been taken up by Dr. Starling, who has shown that the influence 



Fig. 295. En- 

 dosmometer. 



