26 THE BLOOD. 



coagulum had become less firm from that cause. His observations also show 

 that coagulation occurs after poisoning by hydrocyanic acid and in animals 

 hunted to death.. 



Coagulation in different parts of the vascular system is by no means un- 

 usual during life. In the heart, coagula which bear evidence of having existed 

 for some time before death are sometimes found. These were called polypi 

 by some of the older writers and are often formed of fibrin almost free from 

 red corpuscles. They generally occur when death is very gradual and when 

 the circulation continues for some time with greatly diminished activity. It 

 is probable that a small coagulum is first formed, from which the corpuscles 

 are washed away by the current of blood ; and that this becomes larger by 

 farther depositions, until large, vermicular masses of fibrin are found attached, 

 in some instances, to the chordae tendineae. Bodies projecting into the caliber 

 of a blood-vessel soon become coated with a layer of fibrin. , Kough concre- 

 tions about the orifices of the heart frequently lead to the deposition 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. Blood generally coagulates when effused into the 

 areolar tissue or into any of the cavities of the body ; although, effused into the 

 serous cavities, the tunica vaginalis for example, it has been known to remain 

 fluid for days and even weeks, and coagulate when let out by an incision. 

 Coagulation thus takes place in the vessels as the result of stasis or of very- 

 great retardation of the circulation, and in the tissues or cavities of the body, 

 whenever it is accidentally effused. In the latter case, it is generally removed 

 in the course of time by absorption. 



The property of the blood under consideration has an important office in 

 the arrest of haemorrhage. The effect of an absence or great diminution of 

 the coagulability of the circulating fluid is exemplified in instances of what 

 is called the haemorrhagic diathesis, or haemophilia; a condition in which 

 slight wounds are likely to be followed by alarming, and it may be fatal 

 haemorrhage. This condition of the blood is not characterized by any 

 peculiar symptoms except the obstinate flow of blood from slight wounds ; 

 and it may continue for years. 



Conditions which accelerate coagulation have a tendency to arrest haemor- 

 rhage. It is well known that exposure of a bleeding surface to the air has 

 this effect. The way in which the vessel is divided has an important influ- 

 ence. A clean cut will bleed more freely than a ragged laceration. In divis- 

 ion of large vessels, this difference is sometimes very marked. Cases are on 

 record in which the arm has been- torn off at the shoulder-joint, and yet the 

 haemorrhage was, for a time, spontaneously arrested ; while it is well known 

 that division of an artery of comparatively small size, if it be cut across, would 

 be fatal if left to itself. Under these conditions, the internal coat is torn in 

 shreds which retract, their curled ends projecting into the caliber of the ves- 

 sel and having the same effect on the coagulation of blood as a bundle of 

 twigs. In laceration of such a large vessel as the axillary artery, the arrest 

 can not be permanent, for as soon as the system recovers from the shock, 



