R.\nK")-PR(VII',C:i'I\K AC'IIf^X (W Cl'.R'IAIN AMIXKS 



cliHicult. Consequently, counts wi-rc made IVoin films fixed 3 hours after 

 iiradiation. 



RESULTS 



The resuhs of cell counts are show n in Table J. They show that for rat lympho- 

 cytes in vivo there is no significant difTerence between irradiation of the animal 



Table 1. EiTcct ofS-hydroxytryptaminc (0-25 x 10" ^ moles) and cystaminc (0-33x 10^''molrs) 

 on the pyknotic count of lymph nodes 3 hours after irradiation (400 r whole-body dose) 

 in rivo. Effect of increased respired oxygen tension on the radio-protective action. 



The figures represent the means and the standard deviations. Figures in parenthesis 

 indicate the number of nodes examined. 



Both .'j-hydroxytryptamine and cystamine significantly reduce the percentage of pyknotic 

 lymphocytes after irradiation in both air and oxygen (/-"^O-Ol in all cases). 



♦ Oxygen respired at 4 atmospheres absolute pressure. 



in pure oxygen at 4 atmospheres absolute pressure and irradiation carried 

 out in air at atmospheric pressure; both cystamine and 5-OHT in the doses 

 used, give significant protection against irradiation of rat lymphocytes in vivo, 

 whether the animal is irradiated in air at atmospheric pressure or in pure 

 oxygen at 4 atmospheres absolute pressure; whilst oxygen at 4 atmospheres 

 pressure significantly reduces the protective effect of 5-OHT, compared with 

 irradiation in air, no such significant difference was obtained for cystamine. 



The 'oxygen effect', even in the presence of 5-OHT protection is small. 

 However, a series of initial experiments gave results which indicated the 

 trend outlined, and subsequently the experiments were repeated inde- 

 pendently, and confirmed the original findings. 



Throughout the examination of the prepared material, the histological 

 descriptions of Trowell have been confirmed, and similar quantitative 

 variations in counts (standard errors) have been obtained. However, the 

 more detailed descriptions of pyknosis given by Schrek^, using phase contrast, 

 have been recognized in fixed stained material. 



DISCUSSION OF RESULTS 



TrowelP found that the sensitivity of isolated lymph nodes was influenced by 

 oxygen concentrations between and 100 per cent at atmospheric pressure, 



188 



