COAGULATION. x l v 



speedy aggregation of the corpuscles ; it is well known, indeed, that blood 

 may be made to show a buffy coat by delaying its coagulation, but buffed 

 inflammatory blood is not necessarily slow in coagulating. 



Circumstances affecting Coagulation. Various causes accelerate, retard, or 

 entirely prevent the coagulation 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 degrees 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 properties, they become as foreign bodies, and coagulation is 

 promoted. The usual exposure of drawn blood to the air promotes coagula- 

 tion, but according to Lister, by no means so powerfully as has been hereto- 

 fore generally understood. 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 from the escape 

 of liberated gas, whereby more and more of it is successively brought into 

 contact with the sides of the vessel. 



3. Arrest of the blood's motion within the body favours 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 death, blood remains longer fluid in the small veins 

 than in the heart and great vessels ; and even in these the coagulation is 

 usually slow. Agitation of exposed blood accelerates coagulation by in- 

 creasing its exposure to foreign contact. 



4. Water, in a proportion not exceeding twice the bulk of the blood, 

 hastens coagulation ; a larger quantity retards it. Blood also coagulates 

 more speedily when the serum is of low specific gravity, indicative of much 

 water in proportion to the saline ingredients. 



5. Almost every substance that has been tried, except the caustic alkalies, 

 when added to the blood in minute proportion, hastens its coagulation ; 

 although many of the same substances, when mixed with it in somewhat 

 larger quantity, have an opposite effect. The salts of the alkalies and 

 earths, added in the proportion of two or three per cent, and upwards, retard, 

 and, when above a certain quantity, suspend or prevent coagulation ; but, 

 though the process be thus suspended, it speedily ensues on diluting the 

 mixture with water. Caustic potash and soda permanently destroy the 

 coagulability of the blood. Acids delay or prevent coagulation. Opium, 

 extract of belladonna, and many other medicinal agents from the vegetable 

 kingdom, are said to have a similar effect when mixed with the blood ; but 

 the statements of experimenters by no means entirely agree respecting 

 them. 



6. Certain states of the system. Faintness occasioned by loss of blood 

 favours coagulation ; states of excitement are said to have, though not 



