356 BIOLOGICAL EFFECTS OF RADIATION 



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than 3000 A by glass containers and kept at 10°C. ; these were about half 

 inactivated by 1}^ hr. exposure to direct sunlight. 



In contrast to these workers, Jacoby and Jacoby (91) were unable 

 to detect any effect of exposure to June sunshine at Davos, except once 

 when a 2-hr. exposure produced slight inactivation. 



No clear conclusions can be drawn from Ecker's (48) attempt to 

 compare the effects of different parts of the visible and infra-red spectrum, 

 because the relative intensities are not determined. 



No one appears to have determined whether or not oxygen is essential 

 for inactivation by visible light, a matter which would be of considerable 

 theoretical interest. 



Photodynamic Inactivation. — ^Lichtwitz's paper (105) was concerned 

 primarily with photodynamic effects. Eosin was used as a sensitizer, 

 and 8 hr. in direct sunlight reduced the alexin to 20 to 25 per cent of the 

 original value; 16 hr. irradiation reduced its activity to less than 5 per 

 cent. Appropriate tests showed that the specific hemolysin or ambo- 

 ceptor was much more stabile than the alexin in the same or in different 

 sera. Pfeiffer (126) obtained similar results. 



In this connection Noguchi's paper (125) is of very great interest in 

 showing that hemolytic substances such as certain soaps become non- 

 hemolytic except for specifically sensitized cells when dissolved in (heat 

 inactivated) serum instead of water, and at the same time become thermo- 

 labile and sensitive to photodynamic inactivation. The soap-serum 

 mixture is, therefore, an exceedingly good analog of alexin in at least 

 three important respects. The analogy is worth remembering. 



Ultra-violet Radiation. — Bovie's experiments (23) show that sunlight 



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ultra-violet (X2800 to 4000 A) inactivates alexin, since about half the 

 effect of direct sunUght was due to light of wave-length less than 3000 A. 



Baroni and Jonesco-Mihaiesti (13) exposed dilute guinea-pig serum 

 (1 per cent in 0.9 per cent NaCl) in a layer only 1.5 mm. deep to the 

 light of a 110-volt 4-amp. Heraeus quartz mercury arc at 16.5 cm. Its 

 alexin was inactivated in 40 to 60 sec. Undiluted serum, on the other 

 hand, required 17 to 20 min. exposure for alexin inactivation. Alexin 

 was destroyed in about one-sixth of the time required to destroy a rabbit 

 anti-sheep amboceptor of titer 1 : 500. 



Courmont, Nogier, and Dufourt (39) made a similar observation on 

 human serum, and, in addition, found that there was no difference 

 between irradiation in nitrogen, oxygen, air or in vacuo. Small differ- 

 ences would have escaped their attention. 



Abelin and Stiner (1) first observed alexin inactivation under con- 

 trolled temperature conditions (10°C.); earlier workers had, however, 

 satisfied themselves by appropriate controls or otherwise that heating 

 was not a factor in their results. These authors also showed how Bacillus 

 coll, as well as alexin, was protected by thick layers or high concentrations 



