3i8 Heart and Blood V esseis in Edema [Dec. 



of its own. Any change affecting the intracapillary or extra- 

 capillary fluid alters the metabolism of the cells, which in turn in- 

 duces unknown modifications, perhaps of the irritability of the cell. 



As instances of edemas due to venous congestion, Cohnheim 

 mentions cardiac edema, and edema due to venous thrombosis. 

 Pure renal edemas — i. e., when without cardiac complications — are 

 due exclusively to an increase of the permeability of the capillary 

 wall, and are therefore to be considered as inflammatory in their 

 origin. Edema in scarlet-fever nephritis is a clear instance of this 

 kind; an inflammation of the skin causes an increased permea- 

 bility of the walls of the capillaries of the skin. But here, as 

 well as in nephritis, on account of the impaired elimination, the 

 blood contains some toxic agent, which affects the capillary walls. 

 General edemas due to "cold " are caused by irritations of the skin 

 and are, therefore, also of an inflammatory character. The edemas 

 of malaria are brought on by an irritating poison in the blood. 



Hydremia, when chronic, gradually changes, as stated before, 

 the permeability of the capillaries. Hence the edemas of anemia, 

 chlorosis and cachexia. 



The essential factor in the formation of edema is, according 

 to Cohnheim, the increased transudation from the blood, which can 

 no longer be mastered by the lymphatics. Diminished absorption 

 alone is never the essential cause of edema. 



As to the influence of impaired heart action on the genesis 

 of pulmonary edema, Welch's explanation may be mentioned: 

 "A disproportion between the working power of the left ventricle 

 and of the right ventricle of such character that, the resistance 

 remaining the same, the left heart is unable to expel in a unit of 

 time the same quantity of blood as the right heart." And f urther : 

 "It is hardly necessary to State that such factors as changes in 

 osmotic pressure, alterations in the capillary endothelium, interfer- 

 ence with the absorption of lymph, which have become prominent 

 in the later discussions of the causation of edema, may be utilized 

 in the explanations of pulmonary edema, as of congestive edema 

 elsewhere, but I find great difficulty in conceiving any of these 

 factors alone to be the primary cause of acute general edema of 

 the lungs." 



