AEEEST OF BLEEDING. 65 



divided extremities. Owing to the fact that the passage of blood over 

 rough surfaces increases its coagulability (p. 12), a coagulum is formed within 

 the sheath and in front of the cut end by the blood when flowing over the 

 divided surfaces. The comparatively small amount of bleeding wnich_ takes 

 place from arteries that are severed by scraping with a jagged knife, is 

 chiefly due to the increased roughness of the divided parts over which the 

 escaping blood passes. When the bleeding has been stopped by this 

 external coagulum, " an internal coagulum " begins to form within the 

 artery at its cut end, by the continued coagulation of blood. If all goes on 

 favourably, the cut surface at the end of the 'artery, grows together in 

 exactly the same way as in an ordinary wound, and the artery becomes 

 permanently closed by a scar. It must be clearly understood that, accord- 

 ing to the views held by modern pathologists, the thrombus (internal 

 coagulum) takes no more share in the production of the fibrous tissue than 

 does the layer of blood-clot which cements together the surfaces of a 

 wound. The thrombus is replaced by fibrous tissue, but not converted into 

 it. The tendency of the bleeding from an artery to become spontaneously 

 arrested, being proportionate to the comparative quantity of the muscular 

 fibres in the middle coat, will vary in inverse proportion to the size of the 

 vessel. Practically speaking, this natural method of arresting hasmorrhage 

 would be insuflicient to save the animal's life, in the event of division of 

 any of the large arteries. As a rule, an artery which has been cut straight 

 across, will stop bleeding in a shorter time, than if it had been only partly 

 divided ; for in the latter case there will be only slight retraction of the 

 separated parts within the sheath. 



In almost all cases of a cut artery, the end nearest to the heart will be 

 the only one of the two which will require to be closed. The scarlet colour 

 of the blood and the jetting out of that fluid' in harmony with the con- 

 traction of the left^ventricle of the heart, will be characteristic of a 

 wounded artery. 



When an artery is tightly ligatured or twisted, the comparatively brittle 

 internal and middle tunics become ruptured, and their ends retract and turn 

 inwards, so that they offer resistance to the blood flow, and encourage the 

 formation of the internal coagulum ; while the outer coat being strong and 

 t^Jugh, gives an effective support to the ligature, or closes the tube by 

 remaining twisted' on itself, as the case may be. 



Torsion is ppferable to ligature even for large arteries ; for it is less apt 

 to interfere with the healing of the wound, especially if the ligature be not 

 of an antiseptic material which can be readily absorbed, and it can be 

 quickly done by one person. The ligature, if used, should be of such a 

 strength that it will not be absorbed before it accomplishes its special duty 

 of keeping the vessel closed. 



Besides the spontaneous arrest of bleeding by the constriction of the cut 

 end, by its _ retraction within the sheath, and by the formation of an ex- 

 ternal and internal coagulum, the stoppage of haemorrhage will be greatly 

 aided by the animal becoming faint from loss of blood, in which case the 

 rapidity of the flow will be reduced by the action of the heart becoming 

 weaker, and the tendency of the escaping blood to form a. clot will be 

 proportionately increased. 



The application of styptics (oil of turpentine, solution of perchloride of 

 iron, for instance) checks bleeding bj? causing the blood at the seat of injury 

 to coagulate. Hence, before employing them, all blood and clots should be 

 removed from the wound. 



The hot iron stops bleeding by forming at the end of the artery an eschar 

 °l °i"^*'. ^lii* appears, as a rule, to implicate all three tunics. Usuallv 

 the hot iron is more effective in stopping haemorrhage when it is at a dull 

 red heat, than when it is hotter. 



The application of heat or cold through the medium of water, tends to 

 check bleeding by causing contraction of the muscular fibres of the middle 

 coat of the arteries. The contractions produced by the employment of hot 



