422 BACTERIOLOGY. 



modified supplement of the most recent pro- 

 visional administrative instructions." 



While the conditions predisposing to disease 

 which are met with in faulty social conditions 

 and in the general substrata of life, such 

 as air, water, soil and food, act chiefly 

 'upon the human susceptibility to disease, and 

 the improvements made in these particulars 

 diminish this susceptibility, they act in part 

 also by affecting the dissemination of the dis- 

 ease germs. This fact was known long before 

 the days of bacteriology through data of the 

 weightiest kind furnished by epidemiology. 

 In all these matters, however, bacteriology has 

 made us more certain of our ground. Form- 

 erly we could, if we wished, assume with 

 Pettenkofer that cholera was not spread by 

 drinking-water, and could quietly omit reform 

 in this matter from the order of the day. I 

 maintained in 1889, with the unanimous ap- 

 proval of the German association of water tech- 

 nologists and of the international congress of 

 hygiene at Vienna, that the once insoluble 

 question concerning proof of infection with 

 drinking-water after the outbreak of an epi- 

 demic is now a superfluous one, and that we 

 are in a position to convince ourselves before- 

 hand at any moment whether a given source 

 of water makes infection at all possible. We 



