A traveller draws water from an infected, but chemically practically pure well, and marches on, or it may be travels some hundred miles by train. Arrived at his next halting-place, he lowers his drinking vessel into the well he finds there. The amount of matter carried from the infected to the clean well is necessarily far too small to turn the most delicate balance ever constructed, but that same amount would suffice to infect not one, but an indefinite number of wells, so infinitely small are the individual germs concerned carrying the infection. Moreover, the drinking of infected water does not imply certain infection, as at certain stages of digestion the germs are destroyed in the stomachs of healthy people; and hence it is quite possible for the disease to be introduced by a person who has not himself suffered, though perhaps it is more common for it to be caused by mild cases; for it is a mistake to think that cholera is always a fatal or terribly serious disease, as in every epidemic large numbers of cases occur of slight upset of the digestive organs, but which we now know by microscopic examination to be really true cholera. These cases, however, are rarely recognised or recorded, and the really virulent form of the disease, which kills, roughly speaking, half of those it attacks, is alone referred to in ordinary statistics of attacks and deaths. In India, and I suspect in most other semicivilised countries, the commonest method by which wells become infected is by the using of a vessel which has contained infected water to draw water from an uninfected well. The quantity of material required to start the fermentation in a still wholesome well is, as already remarked, infinitesimally minute, and a small drinking vessel and the string used for lowering it into the water, if carried by a traveller from an infected to a healthy place, is amply sufficient, and as the, chemically speaking, still pure water of an infected well is all that is required, it is obvious that no actual fouling of drinking water with the discharges from those stricken down by the disease is either necessary or common. The actual fouling of wells from contiguous latrines or cesspits does no doubt occasionally occur, but owing to the extremely primitive character of Oriental plans of conservancy, is rare.