HEMOSTATIC AGENTS. i6i 



thickened. This result was formerly attributed to rise in blood- 

 pressure, but was regarded by Nothnagel as due to more rapid move- 

 ment of the blood in the vessels in question, and to the resulting 

 increased nutritive supply. 



Hasmostasis by a plug or thrombus is, however, only a provisional 

 measure. Its purpose may be frustrated by suppuration occurring in 

 the walls of the vessel and extending to the clot, which then breaks 

 down : or increasing blood-pressure may drive out the plug, an 

 accident most likel}' to occur where the vessel is injured close to a 

 collateral branch. In such cases secondary bleeding follows. Final 

 closure of the vessel is -only brought about by organisation of the clot 

 and the cicatrix in the tissues surrounding the vessel, and by the union 

 of the walls of the vessel itself. 



Haemostatic agents are very numerous, but of very varying utility. 

 Many have now been entirely discarded; they persisted from pre-anti- 

 septic times, when ligation was only too frequently followed by 

 suppuration with separation and discharge of the ligature. They may 

 be divided into (i) thermic, (2) chemical, (3) mechanical. 



Of thermic agents the most popular is cold ; it is, however, only 

 useful for checking bleeding from capillaries or comparatively 

 insignificant vessels, and even then is uncertain. The result depends 

 on reflex contraction of the walls of the vessel and surrounding 

 tissues checking the flow of blood. When a strong stream of water 

 is used contraction of the tissues is increased by the mechanical 

 stimulus. Heat is usually applied by means of the cautery ; the 

 tissue, together with a portion of the escaping blood, is carbonised 

 and forms a firmly adherent scab which closes the lumen of the vessel. 

 This succeeds well in the case of small vessels, but is of comparatively 

 little value in dealing with the larger. To check bleeding from already 

 existing wounds the cautery should be of a bright red or almost 

 white heat, because a firm scab is required, and one wishes to prevent 

 the cautery adhering to the wound. When, however, it is used to 

 make incisions the instrument should be red and should be moved slowly. 

 Owing to its greater convenience, however, the galvano-cautery has 

 almost entirely replaced the hot iron for removing growths. Although 

 the resulting scab is sterile, and if very small may even undergo absorp- 

 tion, it is impossible to effect primary union between wound surfaces so 

 treated. For this reason the cautery as a haemostatic instrument has 

 largely been discarded, though in castration it is still used to close the 

 divided spermatic artery. It may be remarked in passing that bleeding 

 from hollow organs like the uterus is often best controlled by hot 



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