132 RADIOISOTOPES IN BIOLOGY AND AGRICULTURE 



satisfactory for injection through a venous catheter, collection of urine 

 from a cystostomy tube, or collection of lymph from an indwelling tube 

 in a lymphatic vessel. The cage is made of two endpieces of Lucite plas- 

 tic, 3 by 6 in. Each endpiece has a ^-^-in. hole, one to accommodate a 

 drinking tube and the other for the rat's tail. The floor and sides of the 

 cage are comprised of 14 steel rods, Gj/^ in. long and y^ in. in diameter, set 

 about }/2 in. apart. These rods fit into slots drilled in one endpiece and 

 into holes in corresponding positions in the other endpiece. A 200-g rat 

 is accommodated with the dimensions given. Additional holes or slots 

 may be made for larger or smaller animals. 



RABBITS. Rabbits consistently ingest their own fecal material directly 

 from the anus; this interferes greatly with any study of the absorption or 

 utilization of materials that are administered. This is avoided by collar- 

 ing the animal. Commercial metabolism cages are available which oper- 

 ate on the usual principle of having a wire-mesh floor through which the 

 feces and urine pass onto a finer mesh screen that catches the feces but 

 permits the urine to flow into a funnel arrangement for collection. This 

 type of cage has the inherent disadvantage that some of the feces may not 

 pass through the floor and may be ingested as well as contaminate the 

 skin of the animal. There is also opportunity for considerable cross- 

 contamination between urine and feces. It is helpful to place a raised 

 strainer (made out of hardware cloth) over the urine outlet ; this serves to 

 keep the feces from collecting around the outlet. 



DOGS. Conventional metabolism units are available for the dog similar 

 to those described for the rabbit except that the feces are retained on the 

 floor of the cage. These cages are fairly satisfactory, especially if the 

 animal habitually defecates in one particular area and is on a diet that 

 produces firm stools. Hansard (21) has described a cage which has a cir- 

 cular false floor that supports the animal satisfactorily but still allows 

 the urine and feces to pass through for separate collection. A metabolism 

 mask for dogs has been described by Gaebler (22) which may be suitable 

 for the collection of expired radioactive gases. 



Metabolism and Collection Methods for Farm Animals. Domestic 

 animals will normally be managed under farm conditions until used in the 

 radioisotope studies. The primary problem will be the separate quanti- 

 tative collection of urine and feces for one to several weeks, with the 

 animal subject to a minimum of discomfort. Also metabolism units 

 should allow convenient feeding and watering of the animal and permit 

 the administration of radioisotopes as well as the routine sampling of 

 blood. The units should be relatively inexpensive so that they can be 

 discarded if necessary. However, in several years' experience with the 

 facilities here described, very little if any contamination has occurred. 

 A literature review and detailed discussion of adequate metabolism stands 



