PRECAUTIONS.--The most careful asepsis is essential throughout. Infiltration with novocaine causes no interference with the healing of the wound, and although cases of sloughing of the tissues have been reported after its use, these are almost certainly due to infection of the wound. Care must be exercised also to avoid injecting the drug into a vein. When this accident takes place, the drug is carried at once into the general circulation, and may reach the higher nerve centres in such quantity as to produce serious toxic results. The use of adrenalin calls for special care and thoroughness in securing all bleeding-points, as, after the effect of the adrenalin passes off, even a slight ooze may increase and give rise to a hæmatoma which may jeopardise the healing of the wound. Regional Anæsthesia. In this method of producing anæsthesia, the sensory nerve paths are blocked by injecting the anæsthetic drug into, or around, a nerve trunk. By this procedure complete anæsthesia is produced in the area of distribution of the nerve, and the effect corresponds to a temporary physiological section of the nerve trunk. A temporary motor paralysis is also produced in a mixed nerve. TECHNIQUE.--The solution of the drug must be stronger than that employed for infiltration anæsthesia. A 2 per cent. solution of novocaine in half-strength normal saline with the addition of adrenalin is employed. The injection may be paraneural or intraneural. A _paraneural_ injection is made by passing a needle through the tissues to the known position of a nerve trunk and injecting the anæsthetic around it. The solution gradually diffuses into the nerve tissue, and anæsthesia of the nerve is produced. This method is open to the objection that unless the anæsthetic is accurately placed, no anæsthesia will result, and that in the case of certain nerves there is considerable risk of making the injection into a vein. The latter risk can be avoided by using a glassbarrelled syringe and applying a little suction before the injection is made; if a vein has been pierced, blood will enter the syringe. The _intraneural_ method is more accurate but requires the expenditure of considerable additional time and trouble, and is only employed where other methods of anæsthesia are not feasible. The tissue over the nerve having been infiltrated, the nerve is exposed by open dissection. It must not be pinched by forceps or other instruments, as such manipulations cause severe pain referred to its peripheral distribution. The injection should be made with the nerve lying in its bed by inserting a fine needle in the long axis of the nerve, first into the sheath, which is infiltrated, and then into the nerve itself. The infiltration of the nerve is continued until it presents a fusiform swelling and this may require from 5 to 15 minims of the solution. Complete anæsthesia of its entire distribution usually results in from five to ten minutes.