ANÆSTHESIA OF THE WHOLE ARM.--The nerves of the upper extremity are all derived from the brachial plexus except the intercosto-brachial. This nerve, which is the lateral cutaneous branch of the second intercostal, crosses the axilla and pierces the deep fascia on the medial side of the arm. It supplies the skin on the dorsal part of the medial aspect of the upper arm. The lateral cutaneous branch of the third intercostal nerve sometimes crosses the axilla also, and reaches the medial side of the arm. Injection of the brachial plexus produces complete analgesia of the shoulder and entire arm, and is particularly suited to high amputations and disarticulations at the shoulder. If the area supplied by the intercosto-brachial is encroached upon, this can be anæsthetised by infiltration with a few drams of solution injected subcutaneously along the floor of the axilla from its lateral and posterior borders. METHOD.--The injection may be intraneural or paraneural. The intraneural is made after exposing the plexus by an incision under infiltration anæsthesia from the junction of the middle and lower thirds of the sterno-mastoid to the union of the middle and lateral thirds of the clavicle. It is found lying on the scalenus medius and each of its branches is separately injected with a few drops of 5 per cent. solution of novocaine containing a few drops of adrenalin to the ounce. The paraneural injection is less satisfactory, since the nerves are too large to be readily penetrated in effective quantities by the anæsthetic solution, and since there are numerous veins in the neighbourhood into which the solution may be accidentally injected with dangerous results. The injection is usually made above the clavicle. In this region the plexus lies mainly above and to the lateral side of the third part of the subclavian artery, the lowest trunk lying directly behind the vessel as it rests on the first rib. The position of the artery is first localised with the finger by its pulsations, and the skin and subcutaneous tissue infiltrated immediately above the mid-point of the clavicle. From this point a long fine needle, unattached to the syringe, is passed downwards, backwards, and medially in the direction of the second or third thoracic spine. The distance to which the needle penetrates varies from 2 to 4 c.m. When the plexus is reached a slight radiating pain is felt down the distribution of the radial or median nerve. At this point the needle is held stationary, the syringe attached, and the injection made. The reason for not attaching the syringe earlier is that should the artery be entered, blood will flow. This accident is of little consequence, the needle being withdrawn slightly and introduced a little more laterally. About 10 c.c. of a 2 per cent. solution of novocaine and adrenalin is injected; the needle is then slightly withdrawn and a further 10 c.c. injected in the neighbourhood. Anæsthesia occurs in from three to fifteen minutes.