332 



HISTOLOGY OF THE MORBID PROCESSES. 



no serious result follows. Thrombosis takes place around the em- 

 bolus, but the circulation beyond it is maintained through the anas- 

 tomotic vessels. If, however, the anastomoses are not sufficient to 

 maintain the nutrition of the tissues normally supplied by the ob- 

 structed vessel, those tissues suffer necrosis (Fig. 293). Such a 

 mass of necrosed tissue is called an " infarct." 



Infarcts are divided into anaemic and hsemorrhagic infarcts. The 

 former occur when the tissues are entirely deprived of blood by 

 embolism (Fig. 293) ; the latter take place when, through innutri- 

 tion of the vessels in the part affected by infarction, blood, derived 

 from the veins or through capillary or other fine anastomoses, is 

 permitted to pass into the interstices of the necrosed tissues. 

 These then appear surcharged with blood. The most striking 

 example of hsemorrhagic infarction is that following bland em- 

 bolism of a branch of the pulmonary artery (Fig. 294). 



FIG. 294. 



Haemorrhagic infarct of the lung. (Kaufmann.) The section contains a portion of the 

 plugged vessel beyond the site of the embolus. It and the pulmonary alveoli are filled 

 with blood, which, in the latter, has passed through the capillary walls, rendered per- 

 vious by malnutrition. This blood may be derived from the pulmonary vein and also 

 from the bronchial artery, which communicates with the capillaries of the alveolar walls. 



Phagocytosis. In the preceding pages incidental mention has 

 been made of the ability of leucocytes and other amoeboid cells to 

 incorporate within their cytoplasm particles of foreign matter with 

 which they may come in contact. Such cells within the body are 

 called " phagocytes " (devouring cells). It was at one time thought 

 that these cells had much to do with the killing and destruction 

 of pathogenic bacteria and other organisms that might gain access 

 to the system ; but it is now believed that such is not the case. 



