144 RADIOISOTOPES IN BIOLOGY AND AGRICULTURE 



can be placed (26). An animal consuming the entire pellet will get a 

 quantitative dose. 



Subcutaneous, Intramuscular, or Ifitraperitoneal Injection. These pro- 

 cedures offer no particular difficulty and are made on the immobilized 

 animal. Subcutaneous injections are usually given in the median line of 

 the abdominal wall or in the groin. A fold of skin is pinched up between 

 the forefinger and thumb, and the needle inserted therein. Intramus- 

 cular injections are usually made into the posterior muscles of the thigh or 

 into the lateral thoracic or abdominal muscles. For intraperitoneal injec- 

 tion of smaller animals, the wall of the abdominal cavity is pinched up, 

 care being taken that no intestinal coils are included, and the needle is 

 inserted until it pierces the peritoneum, when the abdominal muscles will 

 be felt to relax. In cattle, sheep, and swine the best point of administra- 

 tion is 6 to 8 in. anterior and ventral to the point of the right hip. 



Intravenous Injection. The lateral tail veins of the mouse are suitable 

 for injection. The tail is immersed in warm (50°C) water for about 

 30 sec. The animal may be conveniently held in a small mailing tube, 

 one end of which is perforated to admit air, the other end being fitted with 

 a cork notched so that the tail can protrude through it. After the mouse 

 is in the tube, the tail is straightened by gentle traction, and the needle 

 (No. 26) is pushed through the skin over one of the lateral veins and then 

 downward into the vein. The radioactive solution can be delivered in 

 the usual way, already described. 



Although many workers use the tail vein and some the jugular for the 

 injection of rats, in our hands the femoral vein has proved most satisfac- 

 tory (Fig. 4-20). The animal is lightly anesthetized and placed on its 

 back. The hair of the hind leg is shaved over the area covering the vein, 

 and a 3^-in. incision made slightly to the right of and parallel to the vein. 

 The skin is rolled over to the left to bring the vein into view. The vein 

 is dilated by compression, and the needle (No. 26 gauge) is passed through 

 the fascia about }--g in. to the left of and parallel to the vein; the needle is 

 then inserted into the vein from the side. After the injection the skin is 

 released and returns to its position covering the vein. Usually suturing 

 is not needed, and the incision may be covered with collodion. 



In guinea pigs a large superficial vein on the medial surface of the hind 

 leg is suitable for injection. Karlson and Feldman (27) have described a 

 technique by means of which it was possible to make daily injections into 

 the ear veins of the guinea pig for 60 successive days. The important 

 feature was transillumination of the ear by means of a Lucite rod with 

 polished ends. A 27-gauge needle was used, and injections were made at 

 the rate of two per minute when the volume injected did not exceed 0.2 ml. 

 The vein along the outer margin of the ear of the rabbit is well adapted for 

 this purpose. It is convenient to immobilize the rabbit by confinement in 



