Hankin described the antibacterial activity of a then-unknown source in the Ganges and Jumna Rivers in India. He noted that "It is seen that the unboiled water of the Ganges kills the cholera germ in less than 3 hours. The same water, when boiled, does not have the same effect. On the other hand, well water is a good medium for this microbe, whether boiled or filtered." He suggested that this unknown source was responsible for limiting the spread of cholera. Some observers have considered this account an early observation of bacteriophage activity. Digital facsimile from the Internet Archive at this link.