648 ADMINISTRATION OP' MEDICINES. 



By a Vein. 



This (intravenous) method of injection, is often practised by 

 veterinary surgeons, but it will certainly be more widely adopted 

 in the near future, on account of its great value in directly attack- 

 ing infective agents in the blood, such as those of septicaemia (p. 

 516). Strict antiseptic precautions (p. 70) should be observed, 

 and great care should be taken to avoid the formation of blood 

 clots and the introduction of air into the vein. Blood clots might 

 form a thrombus (p. 118), and air carried into the heart might 

 easily kill the animal. A small incision into the skin at the seat 

 of operation may be necessary to facilitate the introduction of 

 the needle, and be particularly careful to keep the point of 

 the needle in the centre of the blood-vessel, and not to pierce its 

 other side. Bear in mind that the blood stream in a vein proceeds 

 towards the heart. The jugular vein (p. 118) is the most con- 

 venient one to operate on. The injection should be made very 

 slowly, and its effects should be carefully noted. It is we'J to 

 remember that some medicines, as, for instance, Epsom salts and 

 Glauber's salts, do not have the same action when injected into a 

 vein as they have when taken by the mouth. 



By the Skin. 



When the skin is in a normal condition, its power of absorption 

 as a rule is almost nil ; but when it is inflamed, it can readily take 

 up the active principles of many medicines, as we may see by the 

 irritating effect which extensive cantharides blisters, applied to the 

 legs, have on the kidneys. The antiseptic action of biniodide of 

 mercury on the microbes of pus in more or less deep-seated tissues, 

 when applied to the skin in the form of ointment, with friction, is 

 well shown by the manner in which it checks the formation of 

 abscesses in strangles (p. 458) and joint-evil (p. 519). 



By the Mucous Membrane and Cornea. 



The chief medicines given in this way are cocaine, for deadening 

 pain; and atropine, for dilating the pupil of the eye. 



