346 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 AVidal. 



Increased Hydration Capacity of the Tissue Colloids. — According to 

 Fischer's tlieory 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 tliese 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 tlie proteins, 

 earboliydrates 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 consecjuence 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 Math conditions of 

 asphyxiation, 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 application 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 

 this protein will combine. Presumably the colloidal carbohydrates and 

 lipoids may also play a part in the water absorption of tissues. 



Fischer's theory of edema, in his own words, is this: "A state of 

 edema is induced whenever, in the presence of an adequate supply 

 of water, the affinity of the colloids of the tissues for water is in- 

 creased above that which we are pleased to call normal. The ac- 

 cumulation of acids within the tissues brought about either through 

 their abnormal production, or through the inadequate removal of such 

 as some consider normally produced in the tissues, is chiefly responsi- 

 ble for this increase in the affinity of the colloids for water, though 

 the possibility of explaining at least some of the increased affinity for 

 water tlirough the production or accunnilation of substances which af- 



^0 The secreted fluid of postmortem tlioraeie lymiili How dilVers from normal 

 thoracic lymph in beinp more cloudy, often l)loo<ly. contains more solids, has a 

 liipher molecular concentration with decreased electrical conductivity (Jappelli 

 and d'Errico, Zeit. f. Biol., 1!)07 (.'SO) 1), all of whicli llndiii<rs are in afjreement 

 with the hypothesis that postmortem lymi>h flow dejiends upcm ehanpes in the 

 cells, caused liy as))hyxia and not dissimilar <o the clianjres of acute ne]dnitis. 



