674 



pathogenic fungi and especially on bacteria. Pfeffer^ says, "It seems that 

 all pathogenic bacteria are killed by a sufficient exposure to sunlight." 



That artificial light acts in the same way as sunlight is proved, for 

 example, by the experiments made by Dixon and A\'igham- with radium 

 rays. Cultures made with Bacillus pyocyaneus, B. typhosus, B. prodigi- 

 osus and B. anthracis showed that the fi rays of radium bromid called forth 

 a perceptible arrest of growth. After 5 mg. of radium bromid had acted 4 

 days on the bacteria, at a distance of 4.5 mm., their growth, at least, was 

 stopped, if they were not all killed. 



1 Pflanzenphysiologie, 2d ed., Part II, p. 319. 



2 Dixon, Henry H., and Wigham, J., Action of Radium on Bacteria. Nature, 

 London LXIX; cit. Just's Jahresber. 1903, 11, p. 567. 



