FORMATION OF JAMI'JI 337 



such as lactic acid, which has a large effect in increasing the affinity 

 of tile colloids for water, the cell will, presumably, take on more water, 

 perhaps to a degree to cause intracellular edema. The acids diffusing 

 from the cell into the intercellular spaces or into the lymph will 

 cause equally well an increased affinity for water in the colloids here 

 present, leatling to intercellular edema. Conversely, neutralization 

 of acids present in a colloidal solution, by alkaline salts brought by 

 the blood, will decrease the affinity of the colloids for water which 

 will escape from the colloids as they shrink. 



This theory, which introduces a hitherto unappreciated factor into 

 the considerations of lymph formation and edema, is of the utmost 

 importance. It practically eliminates osmotic pressure, also the cell 

 membranes so essential for the efficiency of this force, and in view of 

 the difficulties that have arisen in trying to fit the cell membrane 

 hypothesis and osmotic pressure to many facts of normal and patho- 

 logical biology, an alternative hypothesis is welcome. As pointed out 

 above, the forces involved in the swelling of colloids are so large as to 

 be of great significance, and the amounts of electrolytes necessary 

 to cause considerable variations in colloidal swelling are not more than 

 can be present under normal and pathological conditions; conse- 

 quently the possible influence of colloidal swelling must be taken 

 into account in all consideration of pathological processes. Whether 

 or not it is capable of as universal application as Fischer maintains, 

 remains to be demonstrated, and there are, indeed, some facts that 

 do not seem to be in harmony with this theory. 



Summary. — We see from the above discussion that numerous the- 

 ories have been advanced to explain the normal formation of lymph, 

 and as their basis exist several different possible factors. Filtration, 

 active secretion by the capillary endothelium, attraction by the tissue- 

 cells, osmosis in response to formation of crystalloids outside the ves- 

 sels, and changes in the affinity of colloids for water; all have been 

 shown to be possible causes of lymph formation. It is highly prob- 

 able that in a certain way all are involved, particularly if we accept 

 the view of the physical school that "secretion" and "attraction" 

 by the cells are merely the outcome of physical forces ; the causes of 

 lymph formation then reduce themselves to absorption, filtration an d 

 diffusion. There has been, until recenth-, no question but that lymph 

 does escape from the vessels through simple filtration, for the pressure 

 inside the capillaries is presumably greater than outside, the capil- 

 lary walls are not water-tight, and the}^ are not impermeable to the 

 substances dissolved in the plasma.^' Likewise osmotic exchanges 



17 Hill ("Recent Advances in Physiolo^iy and Biochemistry," 1000, p. GIS) dis- 

 putes tlie possibility of such a thing as filtration pressure, on the <rroiuid that 

 the structures within the capsule of an orfian must all be under the influence 

 of the blood pressure alike; but with the presence of an outlet for tlie fluid, as 

 in glands with ducts, filtration pressure surely can applv. 

 22 



