24 MANUAL OF EQUINE MEDICINE. 



rapid, the thrombus first appears on the lining membrane of 

 the vessels, and slowly grows from without inwards by- 

 deposit of fresh fibrin, and thus finally blocks up the 

 lumina of the vessels entirely. 



It now extends in a direction towards the heart until it 

 meets a current of blood strong enough to arrest its further 

 progress. 



CAUSES OF THROMBOSIS.— For the coagulation of 

 blood three factors are necessary, viz., fibrinogen, fibrino- 

 plastin, and the fibrin ferment. Fibrinogen exists as 

 such in the liquor sanguinis. The ferment and most of 

 the fibrinoplastin are contained in the white cells, the 

 destruction of some of which is therefore necessary for 

 coagulation. The causes of thrombosis are : 



1. Retarded Blood flow. 



2. Modification of the Vascular Walls ; which consists 

 in abnormality, or removal of the endothelium. 



The causes which produce such modifications are : 



A. Injuries : mechanical, chemical, or physical. 



B. Foreign Bodies : the presence in the vascular system 

 of substances not covered by endothelium, e.g., needles, para- 

 sites, and new growths which have penetrated into the veins. 



C. Such changes in the Blood, or in the supply of blood 

 to a part, as cause disease of the vessel- walls, by imperfect 

 or improper nutrition. 



D. Certain Conditions of the Blood. The tendency to 

 coagulation of the blood is said to be in some measure in- 

 creased in the later months of pregnancy and after profuse 

 haemorrhages. The increased tendency of the blood to 

 coagulate is probably never more than a predisposing cause 

 of thrombosis. 



CHANGES IN THROMBI— These are decolorization 

 (when red), resolution, organization, calcification, softening 

 (simple and infective), and putrefaction. 



