142 KADIOISOTOPES IN BIOLOGY AND AGRICULTURE 



tube. Administration in the feed of mice and rats, etc., is avoided when- 

 ever possible because of the likelihood of spreading contamination around 

 the cage area and because it is difficult to get a good measure of actual 

 intake. However, in some cases this route of administration is necessary, 

 for example, when the experiment calls for a continual intake with a con- 

 stant ratio of radioactivity to some dietary constituent. In this situation 

 the feed should be given in slightly moist condition so as to minimize 

 dusting, and localized barriers can be put around the cages. Also the 

 cage and floor areas should be monitored to give an indication of any con- 

 tamination as soon as it occurs. Incorporation in the drinking water can 

 be accomplished fairly well and is perhaps the method of choice for studies 

 involving the daily dosing of considerable numbers of animals over 

 long periods of time. By the use of commercial graduated drinking 

 tubes, which can be conveniently filled by vacuum devices, it is pos- 

 sible to accomplish a known daily administration with a minimum of 

 contamination. 



The use of the stomach tube is ideal for single dosage to all except the 

 largest species and can even be carried out semiautomatically for routine 

 daily force feeding (24). A convenient semiautomatic arrangement 

 for the routine administration of plutonium solution to rats has been 

 described by Katz et al. (25). For rats, mice, and guinea pigs, small 

 catheter tubing or, even better, a ball-pointed hypodermic needle is suit- 

 able for intubation. A procedure with rats is as follows: The stomach 

 tube is attached by a short piece of rubber tubing to a syringe containing 

 wash solution, as illustrated in Fig. 4-186. The rat is placed on the table 

 with its head facing the operator's right, and the left hand of the operator 

 is spread across the back firmly pressing the animal to the table; the 

 thumb and index finger are placed at the angle of the mouth, giving these 

 two fingers control of the head. Slight pressure by the thumb and index 

 finger will tend to open the jaws, and the stomach tube, moistened with 

 saline, is inserted over the tongue and passed into the stomach, keeping 

 as close to the cheek as possible. If any resistance to the passage of the 

 tube is encountered, it should be withdrawn and reintroduced. When 

 the tube is properly in place, the radioactive solution in the dosing syringe 

 is injected by another person directly into the rubber connection, and the 

 dose is then washed into the stomach with the solution in the wash syr- 

 inge. The stomach tube is then withdrawn. The length of stomach 

 tube required is determined by the size of the animal. If the animal is 

 vicious, it may be wrapped in a towel for easier handling. 



With larger animals both the diameter and the length of the stomach 

 tube to be used are determined by the size of the animal. Stiff-walled 

 plastic or rubber tubing or conventional animal or human stomach tubes 

 may be used. With small volumes it may be convenient to insert and 



