350 BIOLOGICAL EFFECTS OF RADIATION 



now by diluting the bouillon 1:2000 with distilled water they could 

 almost completely detoxicate it in "a few" minutes. 



In the same issue of the Comptes Rendus there is an account of con- 

 siderably more detailed experiments on tetanus-toxin dilutions by 

 Cernovodeanu and Henri (33). The effect of diluting toxic bouillon 

 filtrates with 0.8 per cent NaCl was the same as that observed by Cour- 

 mont and Nogier when they used distilled water. Dilution with fresh 

 nontoxic bouillon decreased the rate of destruction of toxin, presumably 

 because the ratio of protective substance to toxin was increased. A 

 screen of bouillon 5 mm. thick interposed between the source and the 

 toxin to be irradiated prevented inactivation, thus demonstrating the 

 effect of the protective substances in bouillon to be principally at least a 

 result of a purely physical shading of the toxin. Spectrograms showed 

 that the undiluted bouillon had a pronounced absorption for light of 

 X < 2805 A, while there was still considerable transmission of light of 

 X = 2399 A by a similar depth of bouillon diluted 1:100 with 0.8 per cent 



NaCl. 



These facts are of such general significance in all irradiation experi- 

 ments on biological media, especially with ultra-violet light, that they 

 have been given here in some detail. They have also been noticed in 

 studies on alexin, on antibodies, etc., but will be mentioned hereafter 

 only as they bear on some other point of importance. 



Oxygen in Relation to Ultra-violet and Visible Irradiation.— Cerno- 

 vodeanu and Henri (33) also show that irradiation of tetanus toxin in 

 exhausted and sealed quartz vessels still produced inactivation, showing 

 that the reactions induced by ultra-violet radiation can destroy toxin 

 in the absence of oxygen. Inactivation by visible light, on the other 

 hand, depends upon some component of air, presumably oxygen (Tizzoni 

 and Cattani, 158 ; and Tappeiner and Jodlbauer, 155). Other substances 

 such as ricin and tetanus toxin have also been shown by Tappeiner and 

 Jodlbauer to be inactivated photodynamically only when free oxygen 

 is available. In fact, photodynamic processes in general require free 

 oxygen. Why should this difference exist? Does it mean that inactiva- 

 tion by visible light (with or without sensitizers) is an oxidation process, 

 while that by ultra-violet radiation is not? Blum (20) suggests that 

 X < 2800 A may release oxygen from water so that in the presence of 

 very short wave-lengths oxidations may proceed without free oxygen, 

 thus leading eventually to the same end result, namely, in this case 

 oxidation of the toxin. If inactivation is the result of oxidation by the 

 primary splitting of water, ultra-violet radiation acts primarily on water 

 rather than on the toxin. 



Other investigators have added minor details of some interest to our 

 knowledge of the effects of ultra-violet radiation on tetanus toxin. 

 Schubert (142), using a Hanau " Originalhohensonne " (quartz mercury 



