ACTION OF LIGHT ON MICRO-ORGANISMS 385 



The Acttox of Light on the Virulence of 

 Pathogenic Bacteria 



We mentioned on p. 340 that Arloing found inci- 

 dentally that anthrax cultures, after insolation for about 

 30 hours, were not only less virulent when inocu- 

 lated into animals, but that they acted under such cir- 

 cumstances as a sort of vaccine ; guinea-pigs not only 

 surviving inoculation with them, but acquiring also a 

 more or less pronounced degree of immunity towards 

 the, action of virulent anthrax cultures. 



Very few investigations have been made in this 

 interesting and important branch of the subject ; indeed, 

 since the publication of the above observation, made 

 by Arloing in 1885, no experiments in this direction 

 appear to have been undertaken until the year 1891, 

 when Kitasato ^ examined the degree of virulence pos- 

 sessed by the filtrate of tetanus-broth cultures when 

 exposed to the light and dark respectively. This 

 investigator found that in diffused light these tetanus 

 filtrates [i.e.^ the broth from which the tetanus bacilli 

 had been removed by filtration through porous por- 

 celain) by degrees lost their toxic properties ; it was, 

 however, a slow and gradual process, for even after 

 standing from ,nine to ten weeks in diffused light they 

 were still feebly toxic. On the other hand, similar 

 tetanus filtrates preserved in the dark were still, after, 

 being kept for 300 days, as virulent as when they were 

 originally prepared. In direct sunshine, at a tempera- 

 ture of from 35° to 43° C, the toxic properties were 

 entirely destroyed in from 15 to 18 hours. 



This question has been still more recently in- 



^ ' Experimentelle Untersuchungen liber das Tetanusgift,' Zeitsclirift 

 fii/r Hygiene, vol. x., 1891, p. 285. 



C C 



