ABSORPTION. 103 



Starling puts forth the permeability of the capillary wall. The 

 larger the pores in a membrane, the more permeable the membrane 

 will be for the colloids, and the richer the nitrate will be in organic 

 material. This explains the action of the first class of lymphagogues 

 in producing a lymph containing more organic principles than the 

 blood. As to the second class of lymphagogues of Heidenhain, it 

 has been shown that the intravenous injection of sugar or sodium 

 chloride into the circulation causes a large amount of water to leave 

 the tissues and enter the circulation. The high osmotic pressure of 

 the sugar or other crystalloids in the capillaries causes an attraction 

 of water from the tissue-spaces and from the tissues themselves, 

 and, of course, an hydraemic plethora and an increased blood-pres- 

 sure, then the filtration of much lymph, and necessarily one poor in 

 proteids. The amount of lymph produced is dependent solely on 

 two factors: (1) the intracapillary blood-pressure (Ludwig's theory), 

 and (2) the permeability of the endothelial wall of the capillaries 

 of the circulation (Starling's theory). 



Absorption by the Bloodvessels. 



Fluids can be absorbed from the lymph-spaces and from the 

 serous cavities into the blood. This is due to the osmotic pressure 

 exerted by the proteids in the blood for the water in the lymph- 

 spaces. In this way, after a severe haemorrhage, the blood-vessels 

 are rapidly filled by the water absorbed from the lymph-spaces. If 

 there is an excess of fluid in the blood-vessels, part of it is excreted 

 by the kidneys, and part of it passes into the lymph-spaces. 



Quantity of Lymph and Chyle. 



The free interstitial lymph comes in contact with three different 

 elements: the tissues of the organ, the blood of the capillaries, and 

 the lymphatics. Once the lymph is within the lymphatics, none oi! 

 the fluid returns to the spaces of the tissues. 



The quantity of lymph is a varying factor, due to changes in 

 pressure in the capillaries, which, of course, will alter the rate of 

 filtration of the blood-plasma. In digestion, the blood-plasma is 

 charged with the proteids of digestive activity, and consequently the 

 difference of composition between the blood and the lymph will set 

 up osmotic pressures, tending to make each similar in composition. 

 Further changes in the elements of the tissues, whether normal or 

 due to disease, alter the composition of the lymph, and they also 



