194 



RADIOISOTOPES IN BIOLOGY AND AGRICULTURE 



unavoidable movement by the animal and great variation among animals 

 in the thickness of tissue covering the thyroid. Also it is not practical to 

 use multiple-counter arrangements. With cattle the absence of anatom- 

 ical landmarks in the region of the thyroid recjuires the use of a trial-and- 

 error method of measurement. A technique described by Blincoe (67) 

 for in vivo measurements with dairy cattle is as follows: Instrumentation 

 consisted of a 1-in. -diameter end- window Geiger tube, the window of 



Femoral 

 artery ~ 



Lead 

 'Shield 



Capillary 

 bed 



Esferline 

 Angus 

 graphic 

 meter 



Counting 

 rate 



computer 



Femoral 

 vein 



Scaler 



Fig. 5-9. Schematic diagrani of apparatus for contimiovis recording of the disappear- 

 ance of radioactive materials from the circulating blood of dogs. {From William J. 

 Maclntyre and Jack R. Leonards, A Continuous Recording Determination of Radioactive 

 Tracers from Circulating Blood, A'FO-4029, Apr. 21, 1953.) 



which was shielded with 1.27 mm aluminum and the body of which was 

 surrounded by ^ in. lead. The tube was connected to a conventional 

 count-rate meter. With the cow in the stanchion, the dewlap was drawn 

 to one side, and the counter placed against the skin with light pressure in 

 the region of the gland. The counter was moved about to determine the 

 maximum counting rate attainable. The procedure was then repeated 

 on the other side of the neck. A phantom was used for standardization 

 purposes. 



Maclntyre and Leonards (68) have described a method for continuous 

 recording of the disappearance of radioactive materials from the circulat- 

 ing blood of dogs (Fig. 5-9). The right femoral artery was cannulated 

 through rubber tubing to a 3-mm-diameter stainless-steel tube, and the 

 complete circuit established by return to the right femoral vein. The 



