1136 PHYSIOLOGY 



this investment the liver-cells in many places abut on the lumen of the capillary. 

 On injecting the blood-system of the liver the injection is found to run with ease 

 into channels situated within the cells themselves, and it is reasonable to conclude 

 that the blood- plasma takes the same course through these intracellular channels, 

 by which it passes into the lymphatics which lie at the periphery of the lobules. 



In experiments on the lymph production in the limbs alterations 

 of capillary pressure have but slight effect. The lymph-flow from a 

 limb lymphatic is practically unaltered by changes in its arterial 

 supply, although a definite increase may be obtained by ligaturing all 

 the veins of the limb so as to cause a very great rise of capillary 

 pressure. The lymph-flow from the intestines can be measured by 

 collecting the lymph from the thoracic duct. If the lymphatics 

 which leave the liver in the portal fissure be previously ligatured, the 

 whole of the thoracic duct lymph in an animal at rest is derived from 

 the intestines. It will be found that lowering of the capillary pressure 

 in these organs by obstructing the thoracic aorta stops the flow of 

 lymph absolutely, whereas a rise of capillary pressure, such as that 

 produced by ligature of the portal vein, causes a four- or fivefold 

 increase of the lymph. 



The effect of rise of capillary pressure on the lymph-flow is still 

 more striking in the case of the liver. If the inferior vena cava be 

 obstructed just above the opening of the hepatic veins, there is a great 

 fall of arterial pressure, but, owing to the damming back of the blood, 

 a rise of pressure in the liver capillaries to three or four times the 

 normal height. This rise causes a large increase in the lymph-flow 

 from the thoracic duct. The lymph may be increased eight to ten 

 times in amount, and it contains more protein than before. If the portal 

 lymphatics be previously ligatured, obstruction of the inferior vena 

 cava has no effect on the lymph-flow, showing that the whole of this 

 increase is derived from the one region of the body where the capillary 

 pressure is increased, viz. the liver. 



We must conclude that in those regions of the body where the 

 capillaries are fairly permeable the most important factor in lymph 

 production is the intracapillary pressure. 



In the case of the limbs and connective tissues generally, the 

 pressure factor is probably, under normal conditions, of less im- 

 portance, so that the second condition, the chemical, comes here more 

 into prominence. The capillary wall not only permits of filtration 

 under certain pressures but also allows the passage of water and dis- 

 solved substances by diffusion and osmosis. These osmotic inter- 

 changes between blood and cell through the intermediation of the 

 lymph are constantly going on in the normal life of the tissue, and 

 are quite independent of the amount of lymph produced. Thus a 

 gland-cell may use up oxygen, calcium, or sugar, and create a vacuum 



