148 



\i;terinary pathology. 



Retardation of the rate of fJozL'.—A long continued dilata-^ 

 tion of a vessel results in injury especially to the endothelial 

 lining. The injured endothelial cells become swollen, rough- 

 ened and sticky. The leucocytes begin to appear in the peri- 

 pheral portion of the stream, probably because of the libera- 

 tion of some chemic substance by the endothelium that exerts 

 a partial chemotactic action upon the leucocytes. They roll. 



'•4«-- 



•^f' 



„a" ° ^ -P. i»" ° ° ^"° « *= O O „ ^ O OO' 



ocP 





_ o o O 



6 o ^' ~- , t 



OS'r 





tf«^ 



-Dilatid bl 



,"' ssil showing? corpuscles sprtrad throuf;h(mt thi 

 tj jjical ot first slai,') s nf hyiiprrniia. 



tniii1)le, and creep along over the swollen endothelial cells and 

 finalh- adhere to their roughened surfaces. The continued at- 

 tachment of leucocytes to the endothelium diminishes the cali- 

 bre of the vessel and increases the resistance thus retarding 

 the rate of blood flow. 



Oscillation. — The resistance of the flowing blood, due to the 

 roughened endothelium of the vessels and accumulation of 

 leucocytes becomes so increased that the propelling force is 

 momentarily overcome. The blond in the engorged capillaries 

 and arteries may temporarily cease flowing or it mav flow 

 toward the heart, i. e. in the reverse direction during the dias- 

 tolic periods. This to and fro movement is termed oscillation. 



