196 BLOOD. 



atom of albumen separates under the form which we name fibrin ; 

 the fibrin subsequently contracts to the smallest possible volume, 

 just as freshly precipitated silica, alumina, and phosphate of lime 

 gradually contract. If we observe the separation of fibrin in threads, 

 &c., (as described in vol. 1, p. 349), it will appear as if the analogy 

 with hydrated alumina, &c., at all events, affords no special support 

 for this hypothesis, which at first sight is sufficiently plausible. 



The coagulation of the blood the most striking phenomenon 

 presented by fresh blood although for a long time the subject of 

 numerous investigations, is still involved in considerable obscurity. 

 We now recognise fibrin as the proximate cause of the formation 

 of the clot ; we have also, in the introductory portion of this 

 chapter, explained the process of coagulation, in so far as its 

 external phenomena are manifested in healthy blood : but in 

 various physiological and pathological conditions, we meet with 

 numerous anomalies, whose study promises to elucidate the nature 

 of this process. These anomalies, or rather fluctuations of the 

 external phenomena, have reference partly to the duration of the 

 individual periods of coagulation, partly to the final consistence of 

 the clot, and partly to the manner in which the blood-corpuscles 

 are enclosed in it. We shall have to seek for the proximate causes 

 of these modifications, partly in the variable quantity and nature of 

 the fibrin, and in the number and character of the blood-corpuscles, 

 and partly also in the chemical constitution of the serum. 



We shall first notice the variation in the time of coagulating. 

 We much more frequently meet with cases in which the coagula- 

 tion, or one or other of its stages, is delayed, than in which it is 

 abnormally hastened. Tn investigating the causes of this differ- 

 ence, we shall at the same time become acquainted with the phy- 

 siological and pathological relations under which the coagulation 

 proceeds either more slowly or more rapidly than usual. H. Nasse 

 must be especially mentioned, as having devoted very great atten- 

 tion to this department of hsematology, and as having thrown much 

 light upon it by his observations. We must first make mention of 

 certain external relations, which, quite independently of the 

 chemical nature of the blood, exert an influence on the time of 

 coagulation. Among these, we may first notice strong agitation of 

 the blood before, and during the process of coagulation. We 

 find that the separation of the fibrin is more rapidly effected when 

 the blood has been disturbed and shaken, in the same manner as 

 in the case of saturated saline solutions, which deposit their crystals 

 far more rapidly when they have been stirred or agitated. The 



