272 PATHOLOGY OF THE BLOOD AND CIRCULATION. 



engorged with extravasated blood supposed possibly to be 

 due to a back flow from the veins, in which case the final 

 remaining scar is pigmented (Fig. 110). 



(Edema: Normally a certain amount of fluid transudes 

 from the capillary bloodvessels into the interstices of con- 

 nective tissues and the various serous cavities of the body ; 

 when the amount of this fluid is increased or its removal by 



FIG. 109. 



A thrombus in the saphenous vein, 

 showing the projection of the 

 conical end of the thrombus into 

 the femoral vessel. S, saphenous 

 vein; T, thrombus; C, conical 

 end projecting into femoral vein. 

 At v, v, opposite the valves, the 

 thrombus is softened (Virchow). 



Diagram of a hemorrhagic infarct. a, artery 

 obliterated by an embolus (e) ; v, vein filled 

 with a secondary thrombus (th); I, centre 

 of infarct which is becoming disintegrated ; 

 2, area of extravasation ; 3. area of col- 

 lateral hypersemia (O. Weber). 



the veins and lymphatics is lessened the condition is known 

 as oedema or dropsy. The increased transudation may be 

 caused by arterial or venous hypersemia, hydrsemic states of 

 the blood, and possibly by alterations in the walls of the 

 bloodvessels. 



Obstruction of the lymphatic circulation is never a power- 

 ful factor in the production of dropsy ; but venous obstruction 

 is a most important mechanical cause. 



Clinically the chief varieties of cedema are cardiac, renal, 

 cachectic, and angioneurotic. Cardiac dropsy is an example 

 of increased transudation from passive hypersemia, due to the 



