358 



ANNUAL REPORT SMITHSONIAN INSTITUTION, 1933 



(1930); erythema production, Hausser (1928), and Coblentz, Stair, 

 and Hogue (1931) ; and hemolysis, Sonne (1928). The curves rep- 

 resenting bacterial action, virus inactivation, lethal effect on para- 

 moecium, and protein coagulation are of the same general type. The 

 curve in figure 3, showing the radiotoxic spectral sensitivity of a 

 green alga, Ghlorella vulgaris, for which the data were collected here 

 at the Smithsonian Institution (Meier, 1934), resembles the other 

 lethal curves. 



Arnold (1933) reports that the photosynthetic mechanism of a 

 unicellular green alga was destroyed when irradiated at 2537 A. 



S-JiO 2500 



Wave Lenq Xh in A 



F'iGDEB 2. — Relative biological effects with respect to wave lengths, in the ultraviolet below 

 3100 A. Selected from various authors by B. M. Duggar and Alexander Hollaender. 



The chlorophyll either remained unchanged chemically or there was 

 a change so subtle as to escape detection or possibly the ultraviolet 

 rays destroyed a substance other than the chlorophyll. 



The Henris (1912) found that if the action of ultraviolet is not 

 lethal, it may cause profound alteration in the constitution of the 

 organism. They report observations on two new stable forms of 

 Bacillus anthrads, the carrier of anthrax, that were produced by 

 ultraviolet irradiation. One of these two new forms sets up an in- 

 fection that is totally different from that of anthrax. 



Several observers have reported changes in the morphology of 

 bacteria due to ultraviolet irradiation. Generally there is an atten- 

 uation, or, in colored bacteria, a change in the pigment-forming 

 function (Arloing, 1885). 



The stimulative effect of ultraviolet on micro-organisms is more or 

 less obscure at present. Petri (1929) reports that the development 



