152 THE BLOOD. 



supplies it with blood. Many cases are on record, where this 

 has been continued for a number of hours, and a cure 

 effected. 



Bodies projecting into the caliber of a blood-vessel soon 

 become coated with a layer of fibrin. Rough concretions 

 about the orifices of the heart frequently induce the depo- 

 sition of little masses of fibrin, which sometimes become 

 detached, and are carried to various parts of the circulatory 

 system, as the lungs or brain, plugging up one or more of the 

 smaller vessels. These masses have been called by Yirchow, 

 emboli, and have been traced by him, in some instances, from 

 the heart to the situations above mentioned. The experiment 

 has been made of passing a thread through a small artery, 

 allowing it to remain for a few hours, when it is found 

 coated with a layer of coagulated fibrin. 



Blood generally coagulates when it is effused into the 

 areolar tissue, or any of the cavities of the body ; though, 

 effused into the serous cavities, the tunica vaginalis for exam- 

 ple, it has been known to remain fluid for days and even 

 weeks, and coagulate when let out by an incision. In the 

 Graafian follicles, after the discharge of the ovum, we gener- 

 ally have the cavity filled with blood, which forms a clot, 

 and is slowly removed by the process of absorption. 



Coagulation thus takes place in the vessels as the result 

 of stasis, or very great retardation of the circulation, and in 

 the tissues or cavities of the body, whenever it is accidentally 

 effused. In the latter case,dt is generally removed in the 

 course of time by absorption. This takes place in the fol- 

 lowing way : First, we have disappearance of the red cor- 

 puscles, or decoloration of the clot, and the fibrin is then 

 the only element which remains. This becomes reduced 

 from a fibrillated to a granular condition, softens, finally be- 

 comes amorphous, and is absorbed; though when the size 

 of the clot is considerable, this may occupy weeks, and even 

 months, and may never be completely effected. Effused in 

 this manner, the constituents of the blood act as foreign 



