CONDITIONS AFFECTING COAGULATION. 63 



obtained from blood by stirring it with a bundle of small 

 twigs ; and whenever any rough points of earthy matter or 

 foreign bodies are introduced into the bloodvessels, the blood 

 soon coagulates upon them. 



3. Contact with foreign matter, and especially multiplica- 

 tion of the points of contact. Thus, when all other conditions 

 are unfavorable, the blood will coagulate upon rough bodies 

 projecting into the vessels ; as, for example, upon threads 

 passed through arteries or aneurismal sacs, or the heart's 

 valves roughened by inflammatory deposits or calcareous ac- 

 cumulations. And, perhaps, this may explain the quicker co- 

 agulation of blood after death in the heart with walls made 

 irregular by the fleshy columns, than in the simple smooth- 

 walled arteries and veins. 



4. The free access of air. 



5. Coagulation is quicker in shallow than in tall and nar- 

 row vessels. 



6. The addition of less than twice the bulk of water. 



The blood last drawn is said to coagulate more quickly than 

 that which is first let out. 



The coagulation of the blood is retarded by the following 

 means : 



1. Cold retards the coagulation of blood; and it is said that, 

 so long as blood is kept at a temperature below 40 F., it will 

 not coagulate at all. Freezing the blood, of course, prevents 

 its coagulation ; yet it will coagulate, though not firmly, if 

 thawed after being frozen ; and it will do so, even after it has 

 been frozen for several months. Coagulation is accelerated, 

 but the subsequent contraction of the clot is hindered by a 

 temperature between 100 and 120 : a higher temperature re- 

 tards coagulation, or, by coagulating the albumen of the serum, 

 prevents it altogether. 



2. The addition of water in greater proportion than twice 

 the bulk of the blood. 



3. Contact with living tissues, and especially with the interior 

 of a living bloodvessel, retards coagulation, although if the 

 blood be at rest it does not prevent it. 



4. The addition of the alkaline and earthy salts in the pro- 

 portion of 2 or 3 per cent, and upwards. When added in large 

 proportion most of these saline substances prevent coagulation 

 altogether. Coagulation, however, ensues on dilution with 

 water. The time that blood can be thus preserved in a liquid 

 state and coagulated by the addition of water, is quite in- 

 definite. 



