52 Dr. A. Ransome and Mr. S. Delepine. On tie [May 24, 



We have now carried the enquiry a little further, and, 

 amongst other objects, have endeavoured to determine how short a 

 period of exposure to air and light would suffice to destroy the 

 poisonous action of the microbe. We selected guinea-pigs as the 

 most susceptible animals to test this question. 



In the first instance pure cultivations of the bacillus were pre- 

 pared, and were found to be active by frequent inoculations. 

 Small portions of this material were 'spread in a thin layer, 

 upon pieces of sterilized paper. They were arranged in circles 

 of about 2 mm. in diameter, so as to give every opportunity for the 

 action of the elements. They were then exposed in a glass-room, 

 with free access to air and light, z.e.,?close to open windows, for 

 diminishing periods of time, viz., 14, 10, 6, 4, and 2 days respec- 

 tively. Contemporaneous daily records were kept of temperature, 

 maximum and minimum, and of the amount of sunshine taken 

 through the glass roof, by means of one of Negretti and Zambra's 

 sunshine recorders. 



The following table (Table II) gives the results of the meteorol- 

 ogical observations, but as will be seen presently, only those for the 

 first few days are of importance. 



Xo result from the other papers ; the control experiments showing 

 that the bacilli used after this date had lost their virulence. Even 

 the results of Experiments 97 and 98 are doubtful on that account, 

 but Experiment 85 was made with a very virulent specimen, as was 

 proved by the inoculation of two other guinea-pigs, with paper in- 

 fected with the same quantity of the same cultivation, and kept the 

 same length of time, but not exposed to sunlight. In both these cases 

 advanced tuberculosis was produced in 44 days. 



It may be noted that only one of these experiments can be en- 

 tirely relied upon, and that in this case, after 4 days' exposure to 

 air and 12^ hours of sunshine, there was no result from the inocu- 

 lation. 



These observations, though not in any way conclusive,, are in 

 accord with those of Professor Koch,* and they encouraged us to 

 believe that even short exposures of the tubercle-bacillus, even in 

 sputum, to air and light, might render it innocuous. 



In the next series of observations, it was determined to allow 



* Koch, ' Yerhandlungen des International en Medicinisclien Congresses ' (Berlin, 

 4th to 9th August, 1890), vol. 1, p. 35. Koch says that for some years it has 

 become known that light could kill bacteria. He alludes, no doubt, to the ex- 

 periments of Downes and Blunt, Arloing, Boux, and others. Marshall Ward's 

 experiments with the Bacillus Anthracis are still more recent. Koch had been 

 able to confirm this with regard to the tubercle-bacillus, of which cultivations 

 exposed to sunlight might be killed in a space of time varying from a few 

 minutes to some hours. When exposed to cliff use daylight in a room they were 

 killed in from five to seren days. 



