114 THE BLOOD AND THE LYMPH 



replaced by fresh blood before clotting ensues, or it may be that sub- 

 stances derived from the inflamed tissue cause the platelets to aggluti- 

 nate. The increased clotting often observed after the injection of hemo- 

 lytic agencies (foreign sera, snake venom, etc.) may also be due to 

 platelet agglutination. Like the thrombosis following embolism, the 

 clotting occurs at first in the capillaries, the initial thrombi containing 

 masses of platelets along Avith skeletons of blood corpuscles and cells 

 from the blood-forming organs. 



