ACTION OF LIGHT ON MICRO-ORGANISMS 387 



Effect of Sunshine on the Virulence of the Cholera Bacillus 

 suspended in Broth (Palermo) 



Exposure to Sunshine Effect on Guinea-pigs 



. . , , . Animal died in 18 hours. 

 10 min.-2 hours * t . ,, 



(One animal died in 18 hours, but 

 3 hours .... -I another, also inoculated with the 



( same liquid, died after 5 days. 

 3^-4^ hours . . . Remained alive. 



The interesting discovery was further made that 

 those animals which had survived inoculation with the 

 insolated cholera cultures had thereby become protected 

 from the pathogenic action of virulent cholera bacilli, 

 for when 8 days later they were inoculated with the 

 latter, instead of dying, as is usual, in about 18 

 hours, they remained alive. It will be remembered 

 that Arloing claimed to have reduced virulent anthrax 

 cultures to the condition of vaccine by insolation, 

 but, so far as we are aware, Palermo is the only 

 other investigator who has been able to render animals 

 artificially immune to a disease by inoculation with the 

 insolated bacteria. When instead of broth sterilised 

 distilled water was used, the pathogenic properties of 

 the cholera bacillus were more rapidly destroyed (in 

 from 2 to 3 hours) under insolation. 



Palermo also determined the effect of sunshine 

 during the various periods of exposure on the number 

 of cholera bacilli present, as indicated by gelatine cul- 

 tures, but in no instance could any difference in the 

 numbers present be detected. On prolonging the ex- 

 posure to from 6 to 7 hours however, although no effect 

 was produced on the numbers present in the insolated 

 broth cultures, yet the physiological character of the 

 bacilli had undergone considerable modification, for 

 exposure to sunshine was found to have deprived them 



c c 2 



