TflE BLOOD. 479 



Frozen blood may be preserved for an indefinite period, and 

 the property of the fibrine to clot is retained. 



The process of coagulation is favoured by fainting. 

 When blood is flowing freely from an animal, its coagula- 

 bility increases as its quantity in the body diminishes. This 

 is a remarkable provision of nature for the spontaneous arrest 

 of haemorrhage. - It has been said that death by lightning 

 tends to destroy the coagulability of blood. This has been 

 disproved, especially by an observation of Mr Henry Thom- 

 son, which I have heard mentioned by Dr Sharpey. Mr 

 Thomson examined several sheep killed in a thunder-storm, 

 and found that their blood coagulated. Dr Sharpey has also 

 shown that animals that have died of suffocation, contain 

 coagulable blood, contrary to an opinion once generally held. 



Coagulation is impeded by a variety of substances. The 

 generality of materials mixed with blood favour the clotting 

 process, but alkalies check it. Nitrate of potash, sulphate 

 of soda, fec., keep the blood in a fluid state, but if water is 

 added, so as to dilute the salt, the fibrine is observed to 

 solidify. Water added to blood in small quantity accelerates 

 coagulation, but in large amount, stops it. Serum favours 

 the process, and a solution of opium is said to check it. 



Horses' blood presents a singular exception to the normal 

 blood of man and animals in general in the process of coagu- 

 lation. It was observed long since > that the blood of man 

 in inflammatory diseases was attended with the production 

 of a clot, yellow on the surface, and red below. The yellow 

 layer has received the name of ' buffy coat.' Such blood 

 presents also a singular appearance of the surface of the clot, 

 which is concave, and hence termed ' cupped/ The ' buffy 

 coat ' consists of clotted fibrine, with pale corpuscles and a 

 portion of serum ; the red particles in such blood subside. 

 This inflammatory blood has also been termed 'sizy.' It' 



