392 



ANNUAL REPORT SMITSSONIAN INSTITUTION, 19 3 2 



dextrose, becomes especially sensitive to ultra-violet radiation.^^ 

 Most bacteria are destroyed by rays of certain wave lengths less 

 than 313 millimicrons, the bactericidal effect being in proportion to 

 selective absorption.^" 



Bactericidal action. — Ultra-violet rays impair the growth of path- 

 ogenic and nonpathogenic bacteria as well as destroy them.^^ Young 

 cultures have proved to be more sensitive to the rays than old ones. 

 The resistance differs in bacterial individuals of the same culture 

 and in various strains of homogeneous bacteria. The resistance also 

 appears to be different in various bacterial species. Bacteriophages 



FiGUEE 2. — Light effect in percentage of maximum effect : A, curve of skin penetra- 

 tion ; B, curve of erytliema (Hausser and Vablf) ; C, curve of protein light reac- 

 tion ; D, curve of hemolysis ; E, curve of paramecia (Sonne) 



display a notable sensitiveness to the rays, but ferments resist tlio 

 rays better. Bacteria, in dry and pulverized garden earth, have 

 survived exposure to ultra-violet radiation. Ultra-violet rays may 

 destroy bacilli on the skin without causing injury to the latter, this 

 depending much on the individual and local resistance to the rays. 

 The bactericidal action of ultra-violet rays on organisms present 

 in the air can be shown.^^ 



MBurge, W. E., Amer. Journ. Physiol., vol. 36, p. 21, 1915. Hinrichs, M. A., Proc. Soc. 

 Exper. Biol, and Med., vol. 27, p. 535, March, 1930. 



=» Gates, P. L., Journ. Gen. Physiol., vol. 14, p. 31, September, 1930. 



^ Stenstroni, Wilhelm, and Gaida, J. B., Proc. Soc. Exper. Biol, and Med., vol. 28, p. 

 898, June, 1931. 



" Wintersteln, O., Strahlentherapie, vol. 39, p. 619, 1931. 



