Method for Intravenous Injection of Guinea Pigs

A great drawback to guinea pigs as experimental material lies in the difficulty of intravascular injections. Direct cardiac puncture is, of course, readily performed, but much of an injected fluid may escape into the pericardial sac, or the pleural cavity, and the operator be none the wiser. Dosage is well controlled when the jugular vein is used, but this must be bared by incision, and day to day injections are well nigh impossible. To meet the requirements of such work a technique has been devised whereby repeated injections may be made into an ear vein. Most guinea pigs have relatively large ear veins, and those near the margin are extemely superficial. They lie, indeed, so close to the surface that in the attempt to get into them with a needle the vessel is usually transfixed or so torn that hemorrhage obscures .the field. A greater obstacle to the injections is encountered in immobilizing the animal. To accomplish this, the guinea pig is placed in a small wooden box with a U-shaped opening in one end through which the head i~ thrust (Text-fig. 1). Extra space in the box is packed with towelling, and the lid brought down and secured, with a flexible wire, as closely as the #espiration will permit. Fixed firmly to the lid are two thin plates of bone which ~roject horizontally above and to either side of the guinea pig's head. These are platforms to which the ears may be fixed during injection. When needle and syringe are ready, the head is pressed firmly up against the phtforms by an assistant, and one of the ears is drawn over and fastened lightly with a ~ubbercovered spring clamp (Text-fig. 1). Then the injection is made, away from the clamp, into a marginal vein (Text-figs. 2 and 3).