342 EDEMA 



details here, it ma}' be stated that the impression is growing that un- 

 complicated rise in blood pressure is not sufficient by itself to pro- 

 duce edema. Some of the reasons for belittling this factor will be 

 brought out in the subsequent discussion. 



3. Decreased Extravascular Pressure. — This factor is particu- 

 larlj' prominent in the so-called "'edema ex vacuo," which occurs after 

 the absorption of an area of tissue which is so located that the sur- 

 rounding tissues cannot contract or fall in to fill the gap, e. g., brain 

 softening, serous atrophy of fat. A still better example, however, 

 is the edema that follows local decrease in atmospheric pressure in 

 "cupping." In these instances the edema depends partly upon in- 

 creased transudation, and partly on the retention of the fluid in the 

 tissues, because it cannot well leave them against the atmospheric 

 pressure. The idea advanced by Landerer that decreased elasticitj^ 

 of the tissues was a possible cause of edema has been attacked by Bon- 

 niger,-* who found but little alteration in the elasticity of tissues the 

 seat of edema. During the early stages of edema, however, the elas- 

 ticity of the skin may be measurably decreased,-^ even when no edema 

 is demonstrable by palpation; but this is not evidence that any loss 

 of elasticity occupies a causative relation to the edema. The tissues 

 can take up water until as much as six kilos has been added to the 

 Aveight of the entire body before any edema can be detected by pal- 

 pation (Widal). Edema ex vacuo is again an illustration of edema 

 due to purely mechanical causes, but it is of little practical impor- 

 tance. 



4. Increased Permeability of the Capillary Walls. — The im- 

 portance of this factor in the production of edema was first demon- 

 strated by Cohnheim and Lichtheim. who found that the production 

 of an enormous increase in the amount of fluid in the blood (hydremic 

 plethora) by injecting large quantities of salt solution, caused an 

 edema of the viscera and serous cavities, ])ut not any subcutaneous 

 edema until the skin had been irritated by some means, such as hot 

 water, iodin, etc-. By this irritation the ca])illary walls are injured, 

 and an excessive escape of the blood fluids follows, ^lagnus also 

 showed that poisoning with arsenic, which injured the vessels, favored 

 the experimental production of edema by transfusion. Starling, as 

 noted before, observed that the permeability of the ca])illaries varies 

 normally in ditferent organs and tissues, which determines quantita- 

 tive and qualitative ditferences in the lymph normally flowing from 

 various vascular areas. Heidenhain's. "lymphagogues of the fii*st 

 class," which are all poisonous substances, probably act by increasing 

 the permea])ility of the cainllaries, and in this way they produce 

 local iirticaria, which is often observed as a result of iioisoning by 

 these same lymphagogues, e. f/., shellfish and strawhci-iy poisoning. 



aiZoit. oxp. Path. u. Thor., 1005 (1). lU.'^. 

 ssSchade, Zeit. exp. Patli., 1012 (11), 360. 



