lie HEMOSTATIC AGENTS. 



to be thickened. This result was formerly attributed to rise in 

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

 movement of the blood in the vessels in question, and to the 

 resulting increased nutritive supply. 



Haemostasis 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 likely to occur where the vessel is injured close to a 

 collateral branch. In such cases secondary haemorrhage follows. Final 

 closure of the vessel is only brought about by union of its walls, by 

 new formation of connective tissue, and by cicatrisation of the 

 tissues surrounding the vessel. 



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

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

 antiseptic times, when ligation was only too frequently followed by 

 suppuration with separation and discharge of the ligature. They 

 may be divided into (1) thermic, (2) chemical, (3) and surgical. 



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

 useful for checking bleeding from capillaries or comparatively insig- 

 nificant 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 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. Although 

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

 absorption, it is impossible to effect primary union between wound 

 surfaces so treated. For this reason the cautery as a haemostatic 

 instrument has largely been given up, 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 irrigations with water at a temperature of 120° F. 



Most styptics combine rapidly with the blood, and form with it 

 a clot which adheres to the wound and closes the injured vessel. 



