Pathogenesis. 399 



filled by blood from the collateral circulation, and tliis causes 

 more or less marked reddening of the mucosa, which is followed 

 by hemorrhage. 



According to the degree of lowering of the blood pressure, 

 two types of circulatory disturbances in the thrombotic parts 

 may be distingiiished ; there are, of course, no sharp bound- 

 ary lines between these two types. In the milder form the occlu- 

 sion is comparatively small, considering the amount of arterial 

 blood which can still get into the affected territory ; the decrease 

 in the velocity of circulation is not very high; hence the ex- 

 travasation of the blood elements is insignificant and a nutritive 

 disturbance, which can be seen macro scopically does not occur. 

 In the mean time, the arteries supplying the affected territory 

 become dilated, the blood supply soon becomes sufficient, pres- 

 sure and velocity of current become normal again, generally 

 mthin a few hours, and the extravasated elements of the blood 

 are absorbed. In the milder form, therefore, there is always a 

 restitution of the blood circulation to normal conditions. 



The severe form is characterized by very grave nutritive 

 disturbances of all the tissue elements of the intestinal w^all, 

 preferably of the walls of the capillaries and of the mucosa. In 

 consequence of the very considerable retardation of the blood 

 current, the permeability of the capillary walls increases from 

 the second quarter of an hour on, and the blood elements ex- 

 travasate more and more, in increasing amounts, first into the 

 loose tissue of the mucosa, later also into the other tissues of 

 the intestinal wall, to get finally into the intestinal lumen and 

 into the free abdominal cavity. A backward accumulation of 

 venous blood does not take place. A retardation of the lymph 

 current follows the decrease of pressure in the capillaries and 

 the former produces an accumulation of serous fluid in the 

 lymph spaces of the intestinal wall. All this produces an edem- 

 atous-hemorrhagic infiltration in the intestinal wall (infarctus 

 haemorrhagicus). With the profound disturbance of circulation 

 there develops a necrosis of intestinal villi, beginning at the 

 free end and progressing towards the deeper layers of the 

 mucosa. Necrosis of the mucosa may become manifest after 

 two hours, and the deeper layers show the earliest necrotic 

 changes after twenty-four hours ; this indicates that contact 

 with the intestinal contents plays a part in the production of 

 necrosis. 



In some few cases of the severe type the circulatory dis- 

 turbances may disappear, but this, of course, takes a much 

 longer time than in the milder form, sometimes several days. 

 In obstruction of some arteries of the small intestine, a re- 

 establishment of the normal circulation may occur in only the 

 two terminal portions of the bowel, while the hemorrhagic in- 

 farct persists in the median portion. The limit up to which the 

 circulation may be reestablished after a sudden arterial occlu- 

 sion is as follows : Neighboring arteries of the small intestines 



