148 



Distiirhanccs of Circulation. 



variably invade every part of its tissue, causing its destruction by 

 moist gangrene, as is regularly seen in such lesions of the in- 

 testine (septic destruction of the intestine). 



Thrombi, developing in the veins so as to cause their occlusion, 

 of necessity interfere with the passage of the venous blood from 

 the peripher}^, and of course give rise to passive congestion. The 

 duration and termination of such cases also depend upon the 

 presence or absence of proper collateral communications. In case 

 of a partial or complete occlusion of unpaired venous trunks (vena 



Fig-. 15. 



Cicatricial shrinliage after embolism (hfemoi-rhagic infarcts) of the kidney 



of a hog. 



cava, portal vein) or in case of synchronous thrombosis of a num- 

 ber of venous tributaries (veins of the lung) a serious passive con- 

 gestion is occasioned, with stasis of the blood column, hremorrhagic 

 infiltrations or congestive transudations. Should there be a num- 

 ber of collateral branches of sufficient calibre the stagnation of 

 Wood will extend from the point of occlusion only to the first 

 collateral branch, and the blood wull pass without difficulty by the 

 collateral route to the heart ; should the anastomotic passageways 

 be narrow they may become dilated by the pressure of the ob- 

 structed blood and the tissue be gradually relieved of its congestion, 

 provided the degree of dilatation will accommodate the blood ac- 

 cumulated in the various venous channels of the structure. A'ery 

 small veins and the capillaries everywhere in the part may be so 

 distended as to serve the purposes of drainage, thus conducting 



