HANDLING OF RADIOISOTOPES WITH ANIMALS AND PLANTS 147 



on a line drawn from the point of the cartilage to the base of the ear. 

 The needle is guided inward, downward, and backward to the entrance of 

 the thorax between the first pair of ribs to pierce the vena cava at the con- 

 vergence point of the jugular and brachial veins. Large swine are 

 restrained in a standing position, and the same procedure is followed, but 

 with a 23>^^-in. needle. Catheterization can be accomplished as already 

 described. 



Inhalation and Intratracheal Dosage. One of the more difficult proce- 

 dures is the quantitative administration of radioactive materials by the 

 inhalation route. Such procedures are needed to supply important infor- 

 mation on the relative toxicities and absorption from the lungs of insoluble 

 dust suspensions, sprays, volatile compounds, and gases. The apparatus 

 for inhalation studies is specialized and fairly complicated. Various 

 chambers have been described for exposure of laboratory rodents to air- 

 borne contamination (32), exposure of rabbits to hydrogen fluoride (33), 

 and exposure of rabbits to uranium dioxide dust (34). 



Introduction of material directly into the trachea does allow estimation 

 of pulmonary toxicity and removal rate from the lungs. However, such 

 data are not directly applicable to behavior after inhalation. Tracheal 

 administration is relatively simple. The trachea of the animal is sur- 

 gically exposed, and the hypodermic needle is inserted between the rings 

 (Fig. 4-21). The solution should be carefully injected into the lumen of 

 the trachea in rhythm with inhalation by the animal. 



Collection of Blood Samples. In many studies it is necessary to have 

 blood samples for measurement. The following are descriptions of some 

 of the methods: 



A jugular technique for the bleeding of mice has been described by 

 Kassel and Levitan (35) . The animal is held by the loose skin of the back 

 to expose the neck and upper thorax. Several threads of a gauze sponge 

 are caught on the upper incisors, and the sponge is used to hold the head 

 in hyperextension. Depilation from the chin to mid-thorax exposes both 

 external jugulars. A 2G-gauge needle is introduced over the sternum, 

 puncturing the skin 1 to 2 mm below the sternoclavicular junction, and 

 the vessel is approached in a caudocephalic direction. 



With rats, blood may be satisfactorily drawn from the heart. The 

 animal is maintained in a light surgical anesthesia, and the heart is located 

 as the point of maximum palpitation beneath the fourth to sixth ribs. A 

 3^^-in. No. 26 gauge needle and 5-ml syringe are pushed into the thoracic 

 cavity toward the point of throb at an angle of about 45° with the long 

 axis of the body. As the heart is pierced, the plunger is pulled out to 

 draw the blood into the syringe. Amounts of blood up to 1 or 2 per cent 

 of the body weight can be obtained without serious harm to the animal. 

 Smaller amounts may be obtained by free bleeding from a puncture of the 



