656 THEORY OF COAGULATION. 



ever diminishes the chemical function of the lungs, 

 and consequently, the vital properties of the blood, 

 or the process by which it is organized. We also 

 learn from the researches of Denis, Le Canu, and 

 other physiologists, that in all chronic diseases, 

 such as chlorosis, scrofula, diabetes, scurvy, diar- 

 rhea, &c. the blood coagulates slowly and imper- 

 fectly, while in the worst forms of typhus, yellow 

 fever, plague, malignant cholera, tetanus, and hy- 

 drophobia, it scarcely takes place at all, towards 

 their fatal termination. And it is worthy of notice 

 here, that during pregnancy, by which a portion 

 of the vital energy of the mother is expended in 

 support of the foetus, her blood coagulates more 

 slowly than at other periods, giving time for 

 the red particles to subside, thus causing the 

 fibrin to contract by itself on the surface, and to 

 present the appearance of a whitish crust, termed 

 the buffy coat, which is generally witnessed in 



in a proper manner. Accordingly it was observed by Hewson, 

 that whenever the pulmonary circulation is much impeded, the 

 blood first drawn did not coagulate for ten or fifteen minutes ; 

 but that after the congestion of the weakened and overloaded 

 capillaries was removed by taking away a few ounces of blood, it 

 flowed from the orifice more freely, changed from a dark to a bright 

 florid hue, and coagulated in from three to five minutes. It has 

 also been observed by others, that blood which exhibits a bluish 

 tint while flowing, always coagulates more slowly than usual, and 

 afterwards exhibits the buffy coat. I have further observed, that 

 when chickens and rabbits are decapitated under the influence of 

 fright, the blood is more dark than usual, and requires a much 

 longer time to coagulate. 



