It is a good idea to begin on the peripheral part of the vein. Then it is possible to try again nearer the head if the first attempt is unsuccessful. The needle and ear are fixed between the operator's thumb and forefinger. When this has been done, the assistant can stop raising the vein and the injection can begin. For practical reasons, the injection should be performed relatively quickly, and the amount that can be injected is therefore somewhat limited.
Infusion sets are also commercially available, consisting of a tube connected to a needle.
These 'butterfly needles' must be fastened to the skin using adhesive tape or a louse. Their great advantage is the flexibility of the tubing. These sets are available in a variety of sizes, such as 19 and 21 gauge. The animal has been given azaperone as a sedative. This compound has the added advantage of causing peripheral vasodilatation, making the vein more readily accessible.