When the blood is to be given, the delivery tube with the rubber bung is inserted in the flask, and the corpuscles which have gravitated to the bottom are distributed again through the fluid by gently shaking it. In administering the blood, it is very often advisable to inject it through a cannula which is tied into a vein. If the patient is a woman, it will usually be found that the veins are small and buried in fat. Also many transfusions will be given to combat the collapse due to shock and hæmorrhage, in which case the veins will be empty and the use of a cannula will be found essential. Sometimes, however, the patient will have large veins which can be readily distended; this may sometimes be encouraged by keeping the arm for half an hour beforehand in a bath of hot water. Under these circumstances the blood can be given through a needle introduced in exactly the same way as has already been described in the case of the donor. In the following account of the process it will be assumed that the use of a cannula is necessary. When choosing a vein in the patient, the operator must be guided by circumstances. Usually the median basilic will be the most convenient, and if, in a collapsed patient, this is invisible, previous knowledge of the position of the vein must determine the site of the incision. If another operation is being done simultaneously upon the upper part of the patient’s body, it may be more convenient to use the internal saphenous vein in Scarpa’s triangle, or even one of the superficial veins about the ankle. In administering blood to an infant, several methods have been used. These are described separately at the end of the present chapter. [Illustration: Fig. 11.--TRANSFUSION CANNULA (ACTUAL SIZE)] Whatever vein be chosen, the line of the incision is first infiltrated with a small quantity of a 2 per cent. solution of novocain. The vein is then dissected out, and is ligatured near the lower end of the incision. A ligature is also put loosely round the upper part. The operator now takes the barrel of the air-lock, which, together with the attached rubber tube and cannula, is filled with 0·9 per cent. saline solution, all air bubbles being carefully excluded. The tube is clipped near the cannula, so that the whole system, including the cannula, remains filled with the fluid. The form of the cannula used will depend upon the operator’s particular preference, but a type which I have found very convenient is shown in the accompanying figure. It is made of glass, and its extremity is ground down at an angle, which makes it very easy to introduce into the vein. The slight constriction near this end ensures that it can be securely tied into the vein and that no leakage round it shall occur. This is very necessary, because there is sometimes a considerable pressure to be overcome, due to venospasm in a collapsed patient, before the blood begins to flow.