72 HAND-BOOK OF PHYSIOLOGY. 



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



The blood last drawn is said to coagulate more quickly than the first. 

 The coagulation of the blood is retarded, suspended, or prevented 

 by the following means: 



1. Cold retards coagulation; and so long as blood is kept at a tem- 

 perature, 32 F. (0 C.), 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. A higher temperature than 120 F. (49 C. ) retards coag- 

 ulation, 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 blood-vessel. 



4. The addition of neutral salts in the proportion of 2 or 3 per 

 cent, and upward. When added in large proportion most of these saline 

 substances prevent coagulation altogether. Coagulation, however, ensues 

 on dilution with water. The time during which blood can be thus pre- 

 served in a liquid state and coagulated by the addition of water, is quite 

 indefinite. 



5. Imperfect Aeration, as in the blood of those who die by as- 

 phyxia. 



6. In inflammatory states of the system the blood coagulates 

 more slowly although more firmly. 



7. Coagulation is retarded by exclusion of the blood from the 

 air, as by pouring oil on the surface, etc. In vacuo, the blood coagulates 

 quickly; but Lister thinks that the rapidity of the process is due to the 

 bubbling which ensues from the escape of gas, and to the blood being 

 thus brought more freely into contact with the containing vessel. 



8. The coagulation of the blood is prevented altogether by the ad- 

 dition of strong acids and caustic alkalies. 



9. It has been believed, and chiefly on the authority of Hunter, that 

 after certain modes of death the blood does not coagulate; 

 he enumerates the death by lightning, over-exertion (as in animals hunted 

 to death), blows on the stomach, fits of anger. He says, "I have seen 

 instances of them all." Doubtless he had done so; but the results of such 

 events are not constant. The blood has been often observed coagulated 

 in the bodies of animals killed by lightning or an electric shock; and 

 Gulliver has published instances in which he found clots in the hearts 

 of hares and stags hunted to death, and of cocks killed in fighting. 



Cause of the fluidity of the blood within the living body. 

 Very closely connected with the problem of the coagulation of the blood 

 arises the question, why does the blood remain liquid within the living 

 body? We have certain pathological and experimental facts, apparently 



