AUTORADIOGRAPHY 349 



grams were due to the S^^ in the form of nucleoprotein which had been 

 synthesized in the time between treatment with radioactivity and sam- 

 pHng. Figure 7-15 shows a phase-contrast photomicrograph and an 

 autoradiogram of the same section which demonstrates the typical local- 

 ization of S^^ in the chromosomes. 



Leblond et al. (43) have also studied in rats the histological locahzation 

 of newly formed desoxyribonucleic acid that was found in tissues where 

 cell divisions are numerous. P'*'- was used, and all the phosphorus com- 



Fig. 7-15. Autoradiographic appearance of S'^ over a group of chromosomes from a 

 root cell, (a) Phase-contrast microphotograph. (6) Autoradiogram of same field. 

 [Courtesy of S. R. Pelc and A. Howard, Brit. Med. Bull, 8: 132-135 (1952).] 



pounds except desoxyribonucleic acid were removed l)y the fixing and 

 staining procedures plus treatment with ribonuclease. Taylor (44) has 

 also detected the incorporation of P^'- into individual nuclei. The data 

 suggested that the period of P^^ incorporation corresponded to the time 

 of chromosome reproduction and that desoxyribonucleic acid constituted 

 a permanent framework of the chromosome. Lily anthers and Trad- 

 escantia were used as experimental material, and perchloric acid was 

 employed for differential extraction of the phosphorus compounds from 

 the cell. 



Figure 7-16 presents a phase photograph and autoradiogram of a cell of 

 the gastric caecum of Drosophila fixed l}-^ hr after feeding on food con- 

 taining P^- (45). This autoradiogram was prepared by fixation of the 



