LOCAL ANAESTHESIA. 61 



conjunctiva are rendered easy. Five or six subconjunctival injections 

 made around the ball of the eye permit the eye itself to be removed 

 without great pain. Cocaine acts equally well on other mucous 

 surfaces, and under certain conditions may be useful in painful 

 inflammations of these membranes. The most recent experiments 

 appear to show, however, that the blanching and anaesthesia are 

 followed by congestion of the parts, and the use of cocaine in gargles, 

 etc., for inflamed pharynx has been abandoned in human surgery, 

 the after effects being bad. Solution of cocaine, 2 to 5 per cent., 

 is frequently employed subcutaneously to assist in the diagnosis 

 of obscure lameness in horses. 



By a series of small injections along the course of a proposed 

 incision operation is rendered painless, provided the seat of operation 

 be in a mucous membrane or in the skin. A Pravaz's syringe fitted 

 with a long fine needle is used, the needle being inserted into the 

 subcutaneous connective tissue, or, better, into the thickness of the 

 epidermis, following the direction of incision. As the needle is 

 gradually withdrawn the piston is slowly pressed home, leaving the 

 track filled with fluid. The anaesthetic qualities of cocaine are 

 increased by previously injecting morphine. Its toxicity varies 

 according to species. In the dog the dose varies from § to 1£ grains. 

 Strong solutions offer no advantages and are dangerous. Cocaine 

 solutions of whatever strength, lose, more or less completely, their 

 anaesthetic quality on becoming acid, but this can be restored by 

 neutralising the liquid. 



Local Anaesthesia by Infiltration. Schleich produces local anaes- 

 thesia by causing artificial oedema in the region of the operation. 

 He performed amputation and even laparotomy successfully. He 

 showed that it is not necessary to inject strong solutions of the 

 anaesthetics which might produce poisoning, but that quite weak 

 solutions, even a 2 per cent, solution of chloride of sodium, suffice, 

 and that in all cases of anaesthesia, other factors than the mere 

 chemical constitution of the substance play an important part. The 

 injection of fluids under fairly high pressure into the skin and sub- 

 cutaneous tissues renders the whole area affected completely 

 insensitive. Should the tissues be cut through no blood flows. 



This method produces anaesthesia by the co-operation of four 

 factors — the pressure induced by the mechanical action of the liquid, 

 cold due to the temperature of the solution, anaemia caused by the 

 cold and pressure, and a chemical change produced in the nerve 

 endings. The undermentioned formulae, which have been used 

 in human practice, have been tried on horses and dogs by 



