AUTORADIOGRAPHY 



351 



food, the highest concentrations of P^^ were observed in the nucleolus and 

 chromatin. It was postulated that the nucleolus may be a center of RNA 

 synthesis or a reservoir of RNA produced in other parts of the nucleus, 

 possibly the chromatin. Similar studies have been described by Taylor 

 and Taylor (46). 



Emhryonic Development. Autoradiography has been of especial advan- 

 tage in the study of embryology, primarily on account of the difliculty of 



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Fig. 7-17. Autoradiographic appearance of S^° in the 20-day-ol(l rat embryo, (a) 

 Stained section, (b) Autoradiogram showing selective deposition in cartilage. 

 [From Dominic D. Dziewiatkoivski, Sulfate-Sulfur Metabolism in the Rat Fetus as 

 Indicated by Sulfur-35. J. Exptl. Med., 93: 119-128 (1953).] 



precise dissection of newly developed organs and their small mass. Fig- 

 ure 7-17 shows a stained section and S^* autoradiogram of a 20-day-old 

 rat embryo, as reported by Dziewiatkowski (47). It is clear from the 

 autoradiogram that there was considerably more deposition in the skel- 

 eton than in other tissues and that the cartilage showed a higher concen- 

 tration than did the calcified or calcifying regions. The embryo was fixed 

 for 6 days at 25°C in 3.7 per cent formaldehyde, dehydrated in upgraded 

 concentrations of ethanol, cleared in xjdol, and embedded in paraffin, and 

 sections were cut at 7 n. The sections were mounted on microscopic 



