314 BULLETIN No. 161 [November, 



Ki'i'i'XT 01-' LIGHT UPON SPOKI',- AND NONSPORE-BEARING 



ORGANISMS 



A few spore-bearing and nonspore-bearing or- 

 CULTURE organisms were tested by exposing them to the 



direct rays of the sun. The spore-bearing organ- 

 isms, B. subtilis and B. mesentericus viilgatus, were grown upon 

 peptoneless agar (made with three grams of beef extract and fif- 

 teen grams of agar per liter) for six days at 32 C. An examina- 

 tion of the cultures showed an abundance of well-developed spores. 

 The vegetative cells of these two organisms were obtained by re- 

 peated growths in beef broth. The broth cultures were kept at 

 37 C. and repeated every twenty-four hours for six days. A 

 microscopic examination at the end of this time showed no spores. 

 B. diphtheria cultures were obtained from twenty- four hours' 

 growth upon Loeffler's blood serum. All other organisms used were 

 from fresh broth cultures grown at the optimum temperature for 

 the organism tested. 



MANNER OF The- cultures grown on the solid media were sus- 

 EXPOSURE pended in 0.8 percent salt solution. A concen- 



tration of slightly milky appearing emulsion was 

 formed. Then a loop of this emulsion was spread in a very thin 

 smear on either a small slip of sterile glazed paper or a small sterile 

 glass cover. These were then exposed to the direct rays of the 

 sun for definite periods of time between the hours of ten in the 

 morning and three in the afternoon. The exposed slips, with the 

 exception of those containing B. diphtheria, were aseptically drop- 

 ped into sterile broth and incubated at a temperature of 30 C. for 

 one week. The exposed smears of B. diphtheria were seeded on 

 Loeffler's blood serum and incubated at 37 C. for one week. The 

 cultures were carefully examined for growth, and if growth was 

 evident further tests were made to see if it was the same as the 

 original culture or an accidental contamination. 



RESULTS ^ summary of the results is given in Table 8. 



It will be noted that the nonspore-bearing organ- 

 isms were all killed in a few minutes. (*/> to 6 



minutes). While the spore-bearing organisms were not killed in 



the time exposed (180 minutes). 



