346 EDEMA 



There are 3ome difficulties, however, in applying the influence of 

 osmotic pressure as an explanation of all edemas. For example, in 

 edema of the lungs, as Meltzer points out, what is the force that drives 

 the fluid into the empty air-cells? Equally difficult to explain as the 

 result of osmotic disturbance is the distribution of fluid that is seen 

 in cardiac dropsy. The fluid does not accumulate in the tissues where 

 metabolism is greatest, or where the most oxygen is used; but rather 

 in the inactive subcutaneous tissues and in the serous cavities. Possi- 

 bly the original transudation does occur in the muscles and sohd 

 viscera, and the fluid is then mechanically forced out of them into 

 the surrounding tissue-spaces, later settling according to the laws of 

 gravity or according to the distensibility of the tissues. It is im- 

 portant to take into consideration the fact that demonstrable edema 

 does not manifest itself until a very large quantity of fluid has been 

 retained by the body — as much as six kilos, according to Widal. 



Increased Hydration Capacity of the Tissue Colloids. — According 

 to Fischer's theory this factor is of greater importance than any of the 

 preceding, and of chief importance in increasing the amount of water 

 present in the tissues are organic acids formed during metabolism. 

 For example, the great power of asphyxiated muscle to take up water 

 from a strong salt solution, which J. Loeb ascribed to the osmotic 

 pressure of the acids formed in asphyxia, is attributed by Fischer 

 to the influence of these acids upon the capacity of the colloids for 

 water, and this explanation seems to be in better agreement with the 

 facts, especially since Overton has shown that even if all the proteins, 

 carbohydrates and fats in a muscle were split into the greatest possi- 

 ble number of simple molecules and ions, the resulting osmotic pres- 

 sure would not be sufficient to account for the amount of water taken 

 up. Furthermore, when cells with demonstrable semi-permeability 

 die, they at once lose their semi-permeability, and in consequence their 

 osmotic pressure falls — but dead cells and tissues often exhibit great 

 power of taking up water and becoming edematous.^'* It is an in- 

 disputable fact that edema is especially associated with conditions of 

 asphj^xiation, and the attempt to explain this by the increased osmotic 

 pressure of the products of incomplete oxidation seem to harmonize 

 with the facts far less successfully than the apphcation of the prin- 

 ciple of colloidal swelling. A common error of the critics of this 

 theory is that of assuming that free acid must be present to cause 

 swelling. This is not at all true. An amount of acid far less than 

 enough to saturate the acid-binding property of a protein or to be 

 detected by indicators will greatly increase the amount of water which 



" The secreted fluid of postmortem thoracic lymph flow diff"ors from normal 

 thoracic lymph in bein{; more cloudy, often bloody, contains more solids, has a 

 higher molecular concentration with decreased electrical conductivity (.lappelli 

 and d'Errico, Zeit. f. Biol., 1907 (50) 1), all of which findings are in agreement 

 with the hypothesis that postmortem lymph flow depends upon changes in the 

 cells, caused oy asphyxia and not dissimilar to the changes of acute nephritis. 



