386 MICRO-ORGANISMS IN WATER 



vestigated by I'ermi and Pernosi/ who also used 

 tetanus filtrates obtained both from gelatine and broth 

 cultures. In these experiments the temperature during 

 insolation was from 38° to 41° C, and the toxic pro- 

 perties were found to be destroyed by from 8 to 10 

 hours' exposure to sunshine. When^ however, the 

 temperature during insolation was not allowed to rise 

 beyond 37° C. (which was secured by keeping the 

 tubes containing the filtrate immersed in water), it re- 

 quired 15 hours' sunshine to remove the pathogenic 

 properties. On drying, however, the filtrate in a de- 

 siccator and exposing it in Petri dishes to sunshine, 

 100 hours' insolation did not destroy the toxic pro- 

 perties, similar results being obtained when chloroform, 

 ether, benzene, and amyl alcohol were respectively 

 added to the dried filtrate before insolation. 



Palermo ^ has also published some exceedingly in- 

 teresting investigations on the action of sunshine on the 

 virulence of the cholera bacillus when suspended in 

 broth and sterilised distilled water respectively. The 

 initial virulence of all the infected liquids employed, 

 both broth and water, was in each case ascertained 

 before insolation by inoculation into guinea-pigs, and 

 the virulence of the insolated and non-insolated liquids 

 was afterwards similarly determined and compared with 

 that exhibited by the liquids which had been kept 

 under the ordinary conditions, but had not been placed 

 in the sunshine either in protected or unprotected 

 vessels. The following table shows the action of sun- 

 shine on the pathogenic properties of the cholera 

 bacillus : — 



^ * Sul veleno deltetano,' Annali delV Istituto d^ Igiene Sperimentale 

 di Eoma, vol. iv., 1894, p. 8. 



^ * Azione della Luce solare suUa virulenza del bacillo del Colera,' 

 Annali delV Istituto d' Igiene Sperimentale di Boma^ vol. iii., 1893, 

 p. 463. 



