488 PHYSIOLOGY OP THE DOMESTIC ANIMALS. 



horses', oxen's, or dogs' blood, allowing the coagulated albuminoids to remain for 

 at least two weeks under alcohol until they become completely insoluble, filtering, 

 drying over sulphuric acid, and dissolving in water ; traces of albumen which 

 still cling to the ferment may be removed by the cautious addition of acetic acid, 

 or C0 2 . The ferment is not contained in living blood, but is a product of break- 

 ing down white blood-corpuscles. Its amount appears to have no influence on 

 the quantity of fibrin formed, but only on the rapidity of the process. Its activity 

 increases up to the temperature of the body, and the heat of boiling water destroys 

 it ; it may be preserved indefinitely, without losing its activity, at 0° C 



The serous transudations, especially of the horse, since they contain both 

 fibrinogen and fibrinoplastin, but no ferment, coagulate at once on the addition of 

 a drop of ferment solution ; these fluids are, therefore, admirable tests for the pres- 

 ence of the ferment. The same also holds for the still fluid blood which remains 

 in the blood-vessels after death. 



Fibrin is an albuminous body which, in its percentage, composition, and be- 

 havior to most reagents, does not differ from other albuminoids. It may readily 

 be obtained by whipping blood as it flows from a vessel, and then washing the 

 coagulum in water until all the red blood-corpuscles are removed. It then forms 

 a snow-white fibrous mass of the greatest elasticity, this latter property depend- 

 ing on the water contained in its molecular interspaces, for dry fibrin is as brittle 

 as glass. 



Fresh, spontaneously coagulated fibrin contains within its meshes large quan- 

 tities of blood-serum, which are pressed out in the contraction of the fibrin. 



The fibrin formed by the slow coagulation of the plasma of horses' blood 

 possesses a less marked fibrous structure than the fibrin obtained by whipping 

 blood, or even by the coagulation of other mammalian blood. It is rather more 

 of an almost amorphous jelly, which will fracture along any line. 



In hydrochloric acid of from 0.1-0.5 per cent., and in dilute phosphoric, 

 acetic, and lactic acid solutions, fibrin swells up to a transparent jelly, but with- 

 out, to any great extent, passing into solution, unless kept for some time at an 

 elevated temperature, when it is nearly all converted into syntonin and passes into 

 solution. On neutralization it is precipitated, the precipitate being insoluble in 

 water, but readily soluble in very dilute acids and alkalies. Boiled fibrin is 

 entirely insoluble in dilute acids and alkalies, but is partially soluble in the con- 

 centrated acids. 



The cause of the constant fluidity of the blood in the living organism 

 is found in the influence of the normal vascular wall on the blood con- 

 tained in the vessels. That the fibrin factors are not found in the living 

 blood is not a sufficient explanation, for it offers no reason why these 

 substances develop in blood outside of the body. 



Coagulation occurs as soon as contact with the living blood-vessels 

 ceases, or when, through various causes, the walls of the blood-vessels 

 lose their normal properties, from which we might infer that something 

 in the vascular walls prevents the development of the fibrin factors; for 

 injections of fibrinoplastin and the fibrin ferment, or transfusion of "lake- 

 colored" blood, have, as an immediate consequence, the abundant forma- 

 tion of blood-clots even in perfectly normal vessels. 



It is not necessary for the blood to be in constant motion in the 

 vessels to prevent coagulation, for the circulation may be arrested in 

 any part, provided the stoppage does not entail any injury to the walls 

 of the vessels, and the blood still remain fluid. But if any circumscribed 

 injury be made to the walls of a blood-vessel, as by the application of a 

 ligature, even though it be subsequently removed, a deposit of fibrin 

 will occur at that point. 



