SUEGICAL HEMOSTASIA. 529 



face it forms, with the blood, a blackish magma, aad a resisting, 

 strongly-adherent clot in the cavity of the vessel. 



4th. Potential Caustics. — The chemical astringents have gen- 

 erally the same mode of action. Upon being placed in contact 

 with the tissues they enter into combination with their elements 

 and form a coagulum, and it is the presence of this clot which 

 produces the hemostatic effect. They are but little used, how- 

 ever, in veterinary practice. The nitrate of silver, some of the 

 mineral acids, as sulphuric, nitric, or arsenious, or bichloride of 

 mercury, are the potential caustics which are occasionally used, 

 though it should always be with great caution, in view of the 

 possible danger of producing an excessive effect. 



5th. AStual Cauterization. — Cauterization with the hot iron 

 is the oldest and principal hemostatic in use in the surgical treat- 

 ment of the domestic animals, and in many instances may be made 

 to supersede all the chemical agents we have considered, more 

 especially in cases of capiUary hemorrhage. It is applied with 

 the iron heated to a white heat, and laid upon the bleeding sur- 

 face, where it immediately creates a thick, impermeable eschar, 

 adherent to the wound, and offering an insurmountable barrier 

 to the escape of the blood. 



To obtain all the effect desired the woujid must be thoroughly 

 free from all extraneous substances, liquid or solid, that nothing 

 may interfere with the rapid formation of the eschar. The blood 

 should be well soaked out, a plug of oakum firmly pressed upon 

 the wound, and the iron pressed perpendicularly upon the tissues; 

 this rapidly forms the eschar. The apphcation of the cautery 

 must be continued for a few seconds only, on account of its Ua- 

 bility, whUe cooling off, to adhere to the tissues and to the eschar, 

 with the consequent risk of reopening the wound and renewing 

 the hemorrhage upon attempting its removal. It is better if the 

 eschar is not sufficiently thick, after a first application, to renew 

 it a second, or even a third time, always taking the same precau- 

 tions, and being careful to avoid contact with sound tissues. 



In this operation it is essential that the temperature of the 

 cautery should be at its maximum. Half-heated, or cooled off by 

 the blood, not only is the application more painful, but the effects 

 are incomplete and the hemorrhage is hkely to return. If the 

 blood escapes too freely, or coagulates too slowly, the eschar not 

 forming, it may sometimes become necessary to carbonize the 



