490 Veterinary Medicine. 



due to the condition of the blood or of the vessels. The researches- 

 of Buchanan, Schmidt, Hammersten and others, show that two 

 albuminoid elements, fibrinogen and paraglobulin, present in the 

 living blood, and a fibrine ferment mainly derived from the white 

 corpuscles in process of change or destruction, determine power- 

 fully, the formation of fibrine and clot. Hewson, Briicke and 

 Lister have shown that blood may be maintained fluid for many 

 hours in an unimpaired vein, or turtle's heart, though it may 

 have been removed from the body, the important condition being 

 that the vein shall retain its vitality and suffer no derangement 

 of its endothelium. lyister has even shown that blood may 

 remain fluid for many hours in a sterilized glass tube which has- 

 been filled by passing the tube carefully into such a vein without 

 disturbing its lining membrane, or imparting motion to the 

 liquid. In such a case a thin film of coagulum only, forms on 

 the interior of the glass tube. In healthy blood, without addi- 

 tion of any extraneous matter, and kept perfectly still, the 

 plasma and globules retain their integrity, and the former its fluidity 

 for a length of time. But if shed into a basin it coagulates at once. 



a. Changes in the blood. Contact with foreign bodies generally 

 determines this change and prompt coagulation. Transfixing the 

 artery with a needle, even a silver one, the entrance of parasites 

 (actinomycosis, strongyli, filaria), the presence of pus, and of 

 certain infectious microbes and their products, the introduction 

 of solid particles and even of air into the vessels, the transfusion 

 of blood which has been exposed so as to receive aerial germs, or 

 which contains microscopic clots, or the globules of which have be- 

 come modified by contact with a basin or other vessel, even the 

 transfusion of defibrinated blood may cause coagulation. The dan- 

 ger is always greater if the blood is drawn from a different genus 

 and unfitted to live in the blood of the recipient. Disease germs 

 are especially dangerous if adapted to colonize the serosa of the 

 vessel and destroy its epithelium. A decrease of the density of 

 blood, favors coagulation, a lowering of one thousandth rendering- 

 it syrupy, and various chemical agents induce or favor coagulation, 

 thus acetic acid, valerianic acid, alcohol, the salts of iron, and 

 above all the salts of lime act in this way. Very high and low 

 temperatures throw down the fibrine as a grumous precipitate, 

 but the clot remains soft. 



b. Changes in the vessels. Any disturbance or alteration of the- 



