304 STRONTIUM 



obtained. The higher doses produced injuries, and a level of about 

 0.1 /xc/g body weight could be generally satisfactory for tracer work. 



In a study of Sr*^'^" and Th^^" distribution, 1.4 ml of the following solu- 

 tion was injected intraperitoneally into rats: pH 4, 1 per cent citric acid, 

 0.15 M Na+, 15 yuc/ml of Sr^^^", 0.64 ^c/ml of Th^^" (Sr-6). Excreta and 

 tissue samples were covered with concentrated HNO3 and evaporated to 

 near dryness, fresh acid added and evaporated, and this process repeated 

 three to eight times until a light-colored ash was obtained. The residue 

 was made to volume, and aliquots dried for counting with a mica-window 

 tube plus a 110-mg/cm^ absorber for strontium, and w'ith an alpha counter 

 unresponsive to beta particles for thorium. 



In another study, weanUng pigs, about 30 lb, were injected intrave- 

 nously with about 507 jxc Sr^°-Y^° at pH 6 (Sr-7). Tissue samples were 

 wet-ashed in concentrated HNO3, and aliquots counted directly with an 

 end-window tube after a period of 24 days. Bone autoradiograms were 

 prepared as described in Chap. 7. From 0.5 to 5 mc Sr^^ and Sr^°-Y^° 

 have been administered to dairy cows for estimation of the transfer to 

 milk (Sr-8, Sr-9). Five to ten millicuries Sr^^-Y^" was orally administered 

 to yearling steers for long-term studies of retention and possible pathologic 

 responses (Sr-9). Studies have been reported with rabbits and monkeys 

 receiving relatively high dosages, 25 to 1000 nc Sr^° per kilogram body 

 weight (Sr-10, Sr-11). 



A series of soils was prepared to contain about 100 dis/sec/g of oven-dry 

 soil as follows (Sr-12) : Each soil consisted of material that had been passed 

 through a 2-mm screen and then mixed. An aliquot of the soil consisting 

 of particles less than 150 n was suspended in water (1:1), and the radio- 

 activity added. The samples were well agitated, dried for at least 5 days 

 at 70°C, and then reconstituted by thorough mixing. The test soils were 

 placed in plastic-painted 6-in. clay pots on the basis of 1600 g of oven-dry 

 soil per pot. Barley, bean, carrot, lettuce, and radish were grown therein 

 to marketable maturity. Soil was prepared for counting by gentle pul- 

 verizing and spreading uniformly over the surface of a stainless-steel cup. 

 An end-window tube was used, and self-absorption corrections were made. 

 Plant material was dried and ground to pass a 40-mesh screen, and 0.5-g 

 samples counted as above except that no self-absorption corrections were 

 necessary. The radioactive plant material from this experiment contain- 

 ing about 7000 dis/sec/g of dried material was used for feeding experi- 

 ments with rats (Sr-13). For stomach- tube feeding, the dry material was 

 mixed into a paste with water to contain about 500 dis/sec/ml. For 

 pellet feeding, the plant material was added to pulverized commercial rat 

 pellets, mixed to dough consistency with water, cut into sections, and 

 baked until hard. 



Mosquitoes were labeled by the use of 10 to 20 m^tc/ml of Sr^^Cl2 in 



