8 LABORATORY COURSE IN SERUM STUDY 



marginal vein distends. The needle of the syringe is then 

 introduced into the vein, pointing toward the base of the ear, 

 and the material injected, care being taken to avoid the intro- 

 duction of bubbles. When the needle is withdrawn a small 

 piece of absorbent cotton is pressed over the puncture to stop 

 bleeding. It is well to leave this cotton adherent to the puncture 

 when the animal is returned to the cage. 



In injecting guinea pigs intravenously it is necessary to incise 

 the skin of the neck and expose the external jugular vein, and unless 

 a very small needle is used the vein must be tied off after injection 

 has been made. Etherization is needed for this procedure. 



The injection of mice and rats intravenously is difficult, but 

 can be accomplished by rubbing the tail with xylol and holding 

 the mouse so that the tail bends sharply over the edge of the jar. 

 The four parallel veins will then stand out and with care a very 

 fine needle can be introduced into one of them. 



2. INTRAPERITONEAL INJECTIONS 



A rabbit or guinea pig is held back down by an assistant and 

 a small area of the abdominal wall median line clipped and the 

 skin disinfected with alcohol or iodine. A fold of skin and muscle 

 is pinched up with the left hand, and the needle, which should not 

 be too sharp, is cautiously introduced directly into the peritoneal 

 cavity and the injection made. The safest point is the median 

 line below the umbilicus, as in this area there is little danger of 

 puncturing the stomach or large intestine. 



3. SUBCUTANEOUS INJECTIONS 



Subcutaneous injections are made in a similar way, after 

 clipping the hair of the area selected and pinching up a fold of 

 skin, taking care that the needle does not pass into the muscles. 

 Rabbits and guinea pigs are usually injected into the surface of 

 the abdomen, rats and mice at the root of the tail. If there is 

 danger of the substance injected causing ulceration, as in the case 

 of red cells, it is best to inject rabbits under the skin of the back, 

 as this area is less likely to become infected. 



