82 BACTERIA IN DAILY LIFE 



of insolation may not have sufficed to destroy 

 their actual vitality. One of these organisms 

 originally obtained from water has been specially 

 studied in this respect by M. Laurent. If slices 

 of potato are streaked with a small number of this 

 particular bacillus (bacille rouge de Kiel) a magnifi- 

 cent patch of blood-red colour makes its appear- 

 ance in the course of a day or two, but if, on the 

 other hand, similar slices of potato are exposed to 

 three hours' sunshine, a colourless growth subse- 

 quently develops, except where here and there a 

 few isolated spots of pale pink are visible. When 

 the insolation is prolonged for five hours nothing 

 whatever appears on the potato, the bacilli having 

 been entirely destroyed. But this is not all. 

 M. Laurent found that if he took some of the 

 colourless growth and inoculated it on to pota- 

 toes he obtained again, but without insolation, a 

 colourless vegetation in fact, three -hours' insola- 

 tion had so modified the physiological character of 

 the bacillus that a new race had been generated, 

 a race deprived of its power of producing this 

 red pigment. In what numerous directions the 

 character of microbes may be and are being 

 modified, even by simple exposure to sunshine, 

 opens up a wide field for speculation and research, 

 whilst the tractability of these minute and most 

 primitive forms of life, if we only approach their 



