FATE OF TUBERCLE BACILLI OUTSIDE THE ANIMAL BODY 287 



would be protected against drying and injuries from the presence 

 of foul material. This conclusion is well borne out by the litera- 

 ture and by the experimental data given in this bulletin. 



REVIEW AND DISCUSSION OF THE LITERATURE 



THE ACTION OF SUNLIGHT ON BACTERIA 



Historical 



The killing power of sunlight on bacteria was first noted by 

 Downes and Blunt 34 in 1877. They worked with mixed cultures 

 suspended in culture solutions and found that the organisms were 

 killed in a short time, as shown by the solutions remaining clear. 

 Tyndall 150 questioned the results of Downes and Blunt but later 

 published results 151 confirming them. Dudaux 37 (1879) was the 

 first to test the action of sunlight upon pure cultures and thus place 

 the work upon a scientific basis. Arloing 7 (1885) was the first to 

 test the action of light upon pathogenic bacteria (Bact. anthracis). 

 He was also the first to use the electric light in sujcjh experimental 

 work. Feltz 38 (1890) was the first to test the action of light upon 

 tubercle bacilli. The classic works of Buchner 16 and Ward 157 

 (1892-3) deserve special mention. Buchner was the first to ex- 

 hibit the killing power of light in reproducing characters by the 

 growth of the organisms in that part of the Petri dish protected 

 from the sunlight. The organisms are thickly seeded in a solid 

 medium like agar, and the desired characters cut from black paper 

 are fastened over this Petri dish. The organisms exposed to the 

 sunlight are killed ; where protected by the black paper, they grow, 

 forming the letters. Ward called especial attention to the effect 

 of different rays of the sun, which he separated by the use of 

 screens of colored glass and colored solutions. 



There early arose the questions : To what is the killing of bac- 

 teria due? and, Are spores more easily killed than the vegetative 

 cells? Arloing 7 (1885) showed that spores of Bact. anthracis in 

 broth were killed in two hours, while to kill the vegetative cells 

 required from twenty-six to thirty hours. Nocard 104 (1885) sug- 

 gested that during the exposure the spores developed into bacilli 

 and the light acted upon the more sensitive vegetative cells. 

 Straus 141 (1886) apparently confirmed this suggestion of Nocard 

 by exposing anthrax spores in broth and in distilled water. He 

 found that the spores in the broth were killed in nine hours while 

 those in distilled water were not killed in this time. In 1886 Ar- 

 loing 8 repealed his experiments, exposing the cultures on ice so 

 that the spores could not develop, and confirmed his earlier results. 

 Ronx 1 - 5 (1887) finds the explanation in the fact that spores are 

 more readily killed by the action of sunlight in the presence of 



