334 EDEMA 



only 2 per cent, to 3 per cent, of proteins, while lymph from the intes- 

 tines contains 4 per cent, to 6 per cent., and lymph from the liver con- 

 tains 6 per cent, to 8 per cent, of proteins; hence he considers that the 

 liver capillaries are the most permeable, i. e., have the largest pores, 

 so that more of the large colloid molecules can escape from them. The 

 effect of lymphagogues of the first class (peptones, etc.) he attributes 

 to their poisonous properties, and the consequent injury to, and altera- 

 tions in, the capillary wall. The crystalloidal lymphagogues, he 

 believes, act by first attracting fluids from the tissues into the blood 

 with a resulting "hydremic plethora," which in turn leads to in- 

 creased blood pressure and consequent filtration of a watery fluid 

 out of the vessels. He considers, therefore, that the amount and 

 quality of the lymph produced in any part are determined solely by 

 two factors, the intracapillary blood pressure and the permeability of 

 the capillary walls. 



In connection with this question of the permeability of the capil- 

 lary walls, Meltzer suggests that the contractility and irritability of 

 the endothelium may be a potent factor in determining the size of the 

 pores in the capillary walls. When in a tonic condition, the endothe- 

 lium is firmly contracted about the pores, keeping their size small; 

 when the endothelial cells become relaxed by any cause, such as poi- 

 sons, high blood pressure, poor nourishment, etc., the pores are en- 

 larged, and increased escape of fluid results.^" It must be borne in 

 mind, however, that most histologists do not now admit that capillary 

 walls contain pores. 



M. H. Fischer holds that the endothelial cells undergo changes in 

 consistency through changes in the affinity of the cell colloids for wa- 

 ter; especially under the influence of acids the endothelium ma}' be- 

 come much more fluid and of greater permeability. Adolf Oswald^" 

 says that the normal capillary wall is somewhat permeable for the 

 less viscous blood proteins (albumin and pseudoglobulin), and in in- 

 flammation this permeability becomes increased so that the more vis- 

 cous euglobulin and fibrinogen can pass through. 



Osmotic Pressure. — Still another possible factor in causing fluid 

 to leave the vessels is osmotic pressure. Heidenhain refers to this 

 cause the transudation produced by crystalloid lymphagogues, al- 

 though in a rather unsatisfactory manner. As a result of the more 

 recent studies of physical chemistry, and its application to biological 

 processes, we have learned to appreciate the importance of osmotic 

 pressure in cell activities (see Introductory Chapter), and in the 

 question of lymph formation it occupies a particularly important 

 place. We may consider it as follows: In the blood we have certain 

 proportions of readily diffusible crystalloids and of non-diffusible 



"" Evidence of the contractility of capillary walls is discussed by Krogh, 

 Jour. Physiol, 1919 (52), 457. 



"> Zeil. f. exp. Path., 1910 (8), 226. ^ 



