THE BLOOD. 155 



generally co-exist. But the rapidity of the stream greatly affects 

 the rate of coagulation, so that one portion of the same blood 

 coagulates slowly that is drawn quickly, and another quickly that 

 is drawn slowly. 



The appearance of the buffy coat does not arise from the 

 slow coagulation, though increased by it ; because, of two por- 

 tions of the same blood, one has afforded no buffy coat, although 

 it remained fluid at least ten minutes after the buffy coat began 

 to be formed on the others, proving, too, if the buffy coat arise 

 from thinness of the fibrin, as appears from Mr. Hewson's ex- 

 periments, the red particles continuing of their usual weight, that 

 slow coagulation is not altogether dependent on mere thinness of 

 the blood, though generally connected and proportional with it. 

 Yet rapid coagulation, by means of a slow stream when the blood 

 is thin, may prevent the buffy coat, by not allowing time for the 

 difference in the weight of the fibrin and red particles to have 

 effect. Stirring such blood, or receiving it into a shallow vessel, 

 has the same consequence, and the slower the coagulation of thin 

 blood, occasioned, for instance, by rapid bleeding, the greater will 

 be the buffy coat. 



If one portion of the same blood is received into a shallow, and 

 another into a deep vessel, the coagulum of the former is looser 

 and spongy, and the quantity of separated serum less. 



The different cups of blood drawn in an inflammatory disease 

 may vary as to the buffy coat, according to accidental variations 

 in the stream ; but generally it is the first cup that abounds in 

 buff, and the last frequently has none. This occurs when there 

 is no difference in the stream. 1 Therefore, if the buff arise from 

 thinness of the fibrin, we must conclude with Hewson u that its 

 qualities may be changed even during bleeding. Sir C. Scuda- 

 more finds much more fibrin in buffy blood ; and, consequently, 

 that not merely the thinness, as Hewson observed, but the quan- 

 tity, of fibrin may vary during the flow of blood. x 



The greater the strength of the patient and the intensity of the 

 inflammation, the firmer is the coagulum of fibrin and the more 

 cupped its appearance. 



Sir C. Scudamore did not find a buffy coat in blood drawn im- 

 mediately after violent exercise. 



s Hewson, 1. c. p, 90^ l 1. c. p. 52. sqq. 



u 1. C. p. 56. sqq. x 1. c. p. 96. 



