84 BACTERIA IN DAILY LIFE 



endowed with the requisite immunising properties, 

 and animals treated first with the so-called sunshine- 

 cholera-vaccine were able subsequently to with- 

 stand otherwise fatal doses of virulent cholera 

 cultures. Dr. Palermo also found that, besides 

 producing this subtle modification in the character 

 of cholera bacilli, sunshine exerted a remarkable 

 physiological change in these organisms, for when 

 examined under the microscope they no longer 

 exhibited their typical activity, having been de- 

 prived of all powers of movement, whilst those 

 kept during the same length of time in the 

 dark had not abated one jot of their customary 

 mobility. 



But sunshine not only controls in this wonder- 

 ful manner the action of the living bacillus, but 

 it also operates upon the products elaborated by 

 disease organisms. Thus the microbe producing 

 lock-jaw or tetanus may be grown' in broth, and 

 the latter may be subsequently passed through a 

 porcelain or a Berkefeld filter, so that the result- 

 ing liquid is entirely deprived of all germ life. 

 This tetanus-filtrate, as it is called, is endowed 

 with very powerful toxic properties, and it will 

 retain its lethal action even when kept for up- 

 wards of three hundred days, providing it is 

 screened from all light ; but place such filtrates 

 in diffused light, and they lose their poisonous 



