352 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1933 



that the course of the reaction of an 18-hour culture of a bac- 

 terium, Staphylococous aureus^ to the short rays of ultraviolet 

 was the same at each wave length studied. The reaction followed 

 similar curves at all the different wave lengths, but occurred at a 

 different energy level at each wave length. In other words, very 

 different total incident energies were required at different wave 

 lengths to produce similar effects. It is true that with young active 

 bacteria, wide differences in the intensity of the incident ultraviolet 

 energy could not be accurately compensated for by corresponding 

 changes in the exposure times to the irradiation. 



Gates also has observed a wide reaction zone covering the be- 

 havior of cells which are not visibly affected and those which seem 

 to be killed outright by the exposure. Single organisms, appar- 

 ently unaffected by the irradiation, grow and divide regularly on the 

 surface of the nutrient agar, forming typical colonies of seemingly 

 normal bacteria. Other organisms exposed to quickly lethal doses 

 degenerate into ghosts or shadows that are undoubtedly dead. Be- 

 tween these two extremes are the organisms that after irradiation 

 increase in size, especially in length, but do not divide when they 

 reach the normal adult stage, so that long filaments of clear, highly 

 refractile protoplasm are formed that look like spaghetti and may 

 measure 50 to 150 microns. After 2 or 4 hours of motion these 

 cells may (1) begin to degenerate and form ghosts, or (2?) divide 

 by cross fission into a number of large or small units which then 

 degenerate, or (3) pinch off' one or more apparently normal daughter 

 cells at one end, which multiply rapidly to form colonies, while the 

 original filament degenerates. Gates thus demonstrates that ultra- 

 violet rays modify two coordinate functions essential to life, namely, 

 cell division, and growth. By appropriate exposures the one can 

 be temporarily or permanently suppressed, while the other may pro- 

 ceed for hours without hindrance until a limit is reached, and unless 

 the division mechanism is restored, the cell degenerates. 



Ehrismann and Noethling (1932), two German workers, irradi- 

 ated several different species of bacteria under precise experimental 

 conditions and determined a curve of the lethal threshold in the 

 ultraviolet. They found that the sensitivity of the different species 

 of bacteria to the radiation varies; also that there is a variation in 

 the lethal effectiveness of different wave lengths. They also have 

 determined that the sensitivity of the single species to the radiation 

 is less as the bacteria are larger. 



Two mysteries of modern bacteriology that the ultraviolet rays 

 bid fair to elucidate are those of the virus and the so-called " bac- 

 teriophage." The viruses that cause diseases in plants and animals 

 have long caused heated debate among bacteriologists, as there is 



