COAGULATION. 35 



liquor sangnmis, the fibrin being generated in that liquid by the concnn-ence of 

 its two constituents in the way already explained, and separating in form of a 

 solid mass, which involves the corpuscles but allows the serum to escape from it 

 in greater or less quantity. But although the solidification of the fibrin and 

 fonnation of a red clot would undoubtedly take place independently of any 

 mechanical co-operation on the part of the corpuscles, still it must not be for- 

 gotten that the red disks are not altogether indifferent while coagulation goes on : 

 for they run together into rolls, as already described, and the circumstance of 

 their doing so with greater or with less promptitude materially affects the result 

 of the coagulating process. Thus there seems good reason to believe that, as H. 

 Nasse pointed out, one of the causes — and in inflammatory blood probably the 

 chief cause — of the production of the buffy coat, is an exaltation of the natural 

 tendency of the red disks to run together, whereby being more promptly and more 

 closely aggregated into compact masses, they more speedily subside through the 

 liquid plasma. leaA'ing the upper part of it colourless by the time coagulation 

 sets in ; and "Wharton Jones has drawn attention to what he conceives to be 

 another influential circumstance depending like-wise on the corpuscles, in inflam- 

 matory blood, namely, the more rapid and close shrinking of the network, or 

 .'ipongework as he terms it, into which the little rolls of corpiiscles unite, and the 

 consequent expulsion of the great part of the liquor sanguinis from its meshes 

 before the fibrin solidifies, in. which case the mass of aggregated coi-pviscles 

 naturally tends to the lower part of the vessel, whilst the expressed plasma, being 

 lighter, accumulates at the top. Of course it is not meant to deny that more 

 tardy coagulation of the plasma would produce the same result as more speedy 

 aggregation of the corpuscles ; it is well kno^^^l. indeed, that blood may be made 

 to show a buffy coafrCy delaying its coagulation, but buffed inflammatory blood 

 is not necessarily slow in coagulating. 



Circumstances affecting Coagulation. — Various causes accelerate, 

 retard, or entirely prevent the cua.c^ulation of the blood ; of these it 

 will here suffice to indicate the more important and best ascertained. 



1. Temperature. — Cold delays, and at or below 40 def,^rees Fahr. 

 wholly suspends coagulation ; but even frozen blood, when thawed 

 and heated again, will coagulate. ^Moderate elevation of temperature 

 above that of the body promotes coagulation. 



2. Coagulation is accelerated by contact of the blood with foreign 

 matter, such as the sides of the basin or other vessel into which it is 

 drawn. On the other hand, the maintenance of its fluidity is favoured 

 by retention within its vessels or natural receptacles where it is in 

 contact with the natural tissues of the body ; but when the coats of the 

 vessels or other tissues, with which the blood is contiguous, lose their 

 vitality and are altered in their projDcrties, they become as foreign 

 bodies, and coagulation is promoted. The usual exposure of drawn 

 blood to the air promotes coagulation, but according to Lister, by no 

 means so powerfully as was formerly believed. The effect of other gases 

 is the same. Coagulation speedily takes place when blood is subjected 

 to the air-pump, and has therefore been said to occur readily in vacuo, 

 but Lister finds that this is owing to the agitation caused by the 

 bubbling of the blood fi'om the escape of liberated gases, whereby more 

 and more of it is successively brought into contact with the sides of 

 tlie vessel. 



3. Arrest of the blood's motion vifhin the- lochj is said to favour 

 coagulation, probably by arresting those perpetual changes of material, 

 both destructive and renovative, to which it is naturally subject in its 

 rapid course through the system. The coagulation of the stagnant 

 blood after death is also largely to be ascribed to the alteration then 

 ensuing in the coats of the containing vessels. Lister found that, after 



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