342 EDEMA 



hypothesis that a disproportion between the working power of the 

 left ventricle and of the right ventricle may lead to pulmonary edema 

 through pulmonary hyperemia. In the edema of passive congestion, 

 increased blood pressure would seem to be an important factor, and 

 there is no doubt that with an increased pressure of the degree ob- 

 served in such conditions some increase in the hanph flow would 

 result ; but from the evidence at hand it is improbable that the amount 

 of lymph so secreted would ever be more than the lymph-vessels could 

 carry away. Even the added obstruction to lymphatic flow due to 

 pressure upon the lymph capillaries by congested blood-vessels, and 

 the resistance to the lymph escaping from the thoracic duct offered by 

 the increased pressure in the subclavian vein, would not satisfac- 

 torily account for the edema of cardiac incompetence. Not to go into 

 details here, it may be stated that the impression prevails that uncom- 

 plicated rise in blood pressure is not sufficient by itself to produce 

 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- 

 larly prominent in the so-called "ede^na ex vacuo," which occurs after 

 the absorption of an area of tissue so located that the surrounding 

 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 increased transu- 

 dation, 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 elasticity of the tissues was 

 a possible cause of edema has been attacked by Boninger.^^ During 

 the early stages of edema the elasticity 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 weight of the entire body before any 

 edema can be detected by palpation (Widal). Edema ex vacuo is 

 again an illustration of edema due to purely mechanical causes, but it 

 is of little practical importance. 



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 jiroduction 

 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, but not any subcutaneous edema 

 until tlic skin had been irritated l)y some means, such as hot water, 

 iodiu, etc. By this irritation the capillary walls are injured, and an 



2" Zeit. exp. Path. u. Ther., 1905 (1), 163. 

 "Schade, Zeit,. exp. Patli., 1912 (11), 369. 



