2 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 98 



LITERATURE REVIEW 



Several investigators have studied the problem of stimulation of 

 growth resulting from irradiation by short wave lengths of the ultra- 

 violet which are generally considered lethal. The chief difficulty con- 

 sists in the correct control of conditions for a quantitative determina- 

 tion of the stimulating exposure for an organism. 



Gilles (1938), in his treatise of 286 pages on "Effets des Rayons 

 Ultra-violets sur les Yegetaux Superieurs," offers a very comprehen- 

 sive survey of all the research that has been carried on up to 1938 on 

 the destructive and favorable effects of the ultraviolet on both higher 

 plants and microorganisms. This book, supplemented by the review 

 made by Wynd and Reynolds (1935) of all the investigations that 

 have been made on ultraviolet and respiratory phenomena, and by the 

 review made by Sperti, Loofbourow, and Dwyer ( 1937) on the stimu- 

 lative effect of ultraviolet on microorganisms, covers the literature 

 thoroughly. 



In this paper 1 shall mention briefly the principal investigations 

 that have been made on the stimulative effect of short wave lengths 

 of the ultraviolet on microorganisms. 



Chavarria and Clark (1924) found that when certain pathogenic 

 fungi very resistant to ultraviolet were given sublethal exposures of 

 ultraviolet from a quartz mercury arc, they showed marked evidence 

 of stimulation and grew larger than the controls. They observed that 

 the stage of stimulation was brief and that lethal action followed rap- 

 idly in nonpigmented cells, but where pigment formed during irradi- 

 ation, the cell was protected and its whole reaction was slowed down 

 so that the stage of stimulation was relatively prominent and the 

 lethal action was delayed. Fungi that are less resistant to the ultra- 

 violet when treated with sublethal exposures produced feeble colonies, 

 which in a few days grew to the size of the controls and when auto- 

 inoculation of the culture medium occurred, the daughter colonies 

 were unusually vigorous. 



Porter and Bockstahler (1928) report stimulated spore formation 

 in the fungus Colletotrichum when exposed to radiations between 3630 

 and 3650 A. produced by a Cooper-Hewitt mercury arc. 



Stevens (1928), in his researches on perithecia formation in fungi, 

 observed that a "very common, though not universal, effect of irradi- 

 ation is to increase sexual or asexual production if such occurs nor- 

 mally and in some species to induce the sexual stage where it does not 

 occur normally." The exposure was to full radiation from a Cooper- 

 1 [ewitt mercury arc. Half of the colony on the agar plate was shaded 



