342 



RADIOISOTOPES IN BIOLOGY AND AGRICULTURE 



The autoradiogram is also of considerable help in the sampHng of 

 heterogeneous samples for radioactivity measurements. An idea of the 

 magnitude of this problem may be gained merely from inspection of a Ca'*^ 



bone autoradiogram (Fig. 7-7), as discussed 

 in the next section. 



Anatomical Relationships. An illustra- 

 tion is presented in Fig. 7-7 of the relation- 

 ship between the deposition of Ca" in bone 

 and the anatomical structure. The auto- 

 radiogram is of a longitudinal section of the 

 metatarsal bone of a 30-day-old calf that 

 had been given orally about 0.5 mc Ca"*^ 

 and sacrificed 7 days later. The auto- 

 radiogram was made by the apposition 

 method of Lotz et al. (23), as described 

 earlier. It is noted that the extent and 

 nature of the Ca**^ deposition is character- 

 istic and is a reflection of the particular 

 bone structure, as follows: A, heavy and 

 relatively diffuse deposition occurs below 

 the epiphyseal plate, probably as a result 

 of vascularity and increased blood flow in 

 this region which results in optimum con- 

 ditions for the exchange of calcium ions 

 between blood and bone crystals. Also, 

 new bone mineral is formed in this region. 

 Note the absence of this characteristic 

 heavy deposition at the other end of this 

 bone, where there is no epiphyseal plate. 

 B, the subperiosteal accumulation is char- 

 acterized by a sharp line of deposition which is related to the narrow 

 layer of growth cells and the limited blood circulation that occurs in this 

 region. C, the area of endochondral bone growth shows a linear deposi- 

 tion, which, however, is readily distinguished from the periosteal lay-down 

 by its spottiness. D, the region of trabecular bone shows a more gen- 

 eralized spotty distribution at a lower intensity than the areas already 

 mentioned. E, the compact bone of the shaft shows little or no radio- 

 activity, probably as a result of the poor circulation. It would be neces- 

 sary to use longer exposure periods if a study of activity in this region 

 were desired. 



Figure 7-8 presents a similar autoradiogram except that it is from an 

 older animal. However, the general features are the same. In addition, 

 it is possible to observe the deposition corresponding to the Haversian sys- 



(a) ib) 



Fig. 7-6. (a) F'ilter-paper chro- 

 matogram of butanol extract of 

 plasma containing added thyrox- 

 ine, with color developed by 

 diazotized sulfanilic acid. (6) 

 Autoradiogram of same chro- 

 matogram resulting from I^^i- 

 labeled substance present in 

 plasma. [From Alvin Taurog, 

 I. L. Chaikoff, and W. Tong, The 

 Nature of Plasma Iodine as Re- 

 vealed by Filter Paper Partition 

 Chromatography, J. Biol. Chem., 

 184: 99-104 (1950).] 



