AUTORADIOGRAPHY 



353 



firmed these findings and, along with histological evidence, led to the 

 hypothesis that the fluorine probably caused an increased rate of bone 

 resorption in the primary and secondary spongiosa, in addition to causing 

 a retardation of bone growth by an effect manifested in the region of 

 hypertrophied cartilage cells. 



There are numerous examples in the literature of the use of autoradio- 

 graphic methods for the study of various pathologic conditions, partic- 

 ularly thyroid neoplasms (54). Some specific applications are as follows: 

 P^^ S^^ and C^^ in callus culture of Sequoia sempervirens (55); absorption 

 of S^* by fungus-infected leaves (56); localization of C'''-labeled tobacco 



Fig. 7-19. Relation of optical densities (values less th.ui 1) and concentrations of Ca'^ 

 (expressed as counts per minute), as determined by radioassay in comparable areas of 

 sheep femurs. (Courtesy of W. E. Lotz.) 



mosaic virus antigen (57) ; P'^^ in tooth cavities (58) ; P^- in cerebral 

 tumors (59); S^^ in chondrosarcomas (60). 



Quantitative Aspects. In general, the greater the concentration of a 

 radioisotope in a tissue, the greater will be the blackening of the emulsion 

 exposed to it. However, the difficulties in obtaining accurate measure- 

 ment of radioactivity from autoradiograms have been formidable indeed, 

 primarily on account of the inherent variables. Lotz (61) has had rea- 

 sonable success in correlating the optical densities of gross bone auto- 

 grams, obtained by use of a densitometer, with radiochemical assays of 

 the same region. It was necessary to expose the samples on the same 

 piece of film and to compare only the same anatomical regions. Figure 

 7-19 presents a series of Ca^^ autoradiograms from sheep that had received 

 different hormone treatment. The values given in the illustration rep- 

 resent the optical density and the counts per minute of Ca^^, as measured 

 with a Geiger counter on a sample taken from the region used for den- 



