1QI2\ FATE OF TUBERCLE BACILLI OrTsini: THE ANIMAL BODY 2<>3 



The difference in killing power is due to the difference in ultra 

 violet light. These rays are largely absorbed by the atmosphere, 

 especially when laden with moisture. According to Langiey, only 

 39 percent of the ultra violet light reaches the sea level. The 

 higher the altitude, the dryer the atmosphere, the more intense is 

 the light and the greater its killing power. 



Mitchell and Crouch found that tubercle bacilli in sputum were 

 not killed in 35 hours, but were killed in 45 hours. These experi- 

 ments are not comparable with the experiments of Treskinskaja, 

 done at nearly the same altitude, since the soil and sputum give 

 far more protection than exposure in a thin layer on glass from a 

 one-percent peptone solution. 



DISCREPANCIES ^ ' ls not to ^ e ex P ect ed that tubercle bacilli under 

 IN RESULTS different conditions will be killed in the same 

 length of time. It is indeed difficult to expose 

 different pure cultures under the same conditions. There may be 

 a difference in the age of the culture, in the uniformity of the 

 emulsion, in the manner of exposing, and in the means of deter- 

 mining the time of killing the germs. When exposed on threads 

 of linen or silk some of the germs may be well protected and live 

 for a much longer time than when exposed in a thin layer on a 

 glass slip or on sterilized glazed paper. Then if the material in 

 which they are exposed, as sputum, is of such a nature as to give 

 protection from drying as well as from the rays of the sun, the 

 difference will be still greater. This accounts, partly at least, for 

 the difference in the results of Sawitsky 128 , which showed that 

 tubercle bacilli in sputum on linen threads lived two and one-half 

 months, and the fact reported by Weinzirl 160 , that a pure culture 

 in thin layers exposed directly to the sun was killed in a few min- 

 utes. It is not possible to give definite reasons for all the discrep- 

 ancies found in the results shown in Table 2 ; but excepting those 

 of Feltz 38 , whose material mixed in the soil might well give com- 

 plete protection from the sun, it will be seen that tubercle bacilli 

 exposed to the sunlight are killed within a few minutes to a few 

 hours. 



DIFFUSE LIGHT It takes ten to fifteen times as long for tubercle 

 bacilli to be killed in diffuse light as in direct sun- 

 light; yet these germs are killed much sooner in diffuse daylight 

 than in the dark, when under the same conditions otherwise, as 

 may be seen by comparing the results of Rickards, Slack and 

 Arms 119 , Twichell 149 , and Ransome and Delepine 114 . 



Tables 2 and 3, respectively, give in brief the literature upon 

 these subjects. 



