SURGICAL HEMOSTASIA. 537 



needle passed under it. Sometimes this is easily done, but in 

 other cases the density of the connective tissue surrounding the 

 artery is too great to allow the needle to pass readily under it, 

 in which case the obstacle can be removed by scraping it away 

 with the finger-nail, which will obviate the application of extra trac- 

 tion upon the vessel. The ligature can then be adjusted around 

 the vessel by means of the tenaculum, and the operation completed 

 as usual. 



(b) Mediate Ligature. — This operation comprises including 

 in the ligature of the vessel a certain portion of the surrounding 

 tissue — a portion which should be as small as possible. 



It is done with a cui-ved needle and a ligature of single or 

 double waxed thread or sUk. The needle is introduced into the 

 thickness of the tissues, at a small distance from the artery, and 

 passed around it with the Ugature, which should be firmly tied in 

 the usual way. 



The ligature is quite painful in consequence of the pressure it 

 makes upon the nervous fibres which accompany the artery, and it 

 is less safe than the immediate operation, exposing the vessel dur- 

 ing its performance to the risk of wounds from the needle, and 

 requiring, besides, a stronger traction upon the ligature and the 

 knot, from the increased bulk of tissues involved ; and there is, 

 again, great uncertainty as to securing a sufficient division of the 

 internal and middle coats of the artery. For these reasons it is 

 less adapted to large than to small arteries. 



The effects produced by the application of a ligature are not 

 wholly mechanical. It is also followed by certain peculiar changes 

 in the condition of the vessel, and by specific inflammatory phe- 

 nomena which result in the permanent obUteration of the tubular 

 character of the artery. 



When an artery is tied with the Ugature the internal and mid- 

 dle coats of the vessel are also divided by the compressing thread, 

 and by their retraction above and below it they form a double 

 cone, the apices of which rest on the ligated spot, the external 

 coat resisting and arresting the flow of the blood. A clot is then 

 formed, and the irritation produced by the pressure of the ligature 

 stimulating the proliferation of the cellular elements of the walls 

 of the vessel, adhesions are soon established between them and 

 the coagulated blood, and the termination is the solidification of 

 the former tube. 



