In 1907 I had the honour of reading a paper before this Society in which a new genus of iron-bacteria was described. This organism was first discovered in Renfrew, near Glasgow, and subsequently observed in various samples of iron-water from different parts of the country. At Renfrew this organism was at the time of its discovery the sole bacterial occupant of the ironwaters of this neighbourhood. In most samples of these waters—and I have examined hundreds—only the remains of iron-bacteria can be obtained, but occasionally the samples are found to contain iron-bacteria in process of growth and multiplication. After a little experience, it is possible to ascertain which streams contain iron-bacteria in this favourable condition. At Renfrew such streams were then common, and so gave me an opportunity of tracing the life-history of this species. The results of this investigation seemed to me to justify the conclusion that I had obtained a new genus of iron-bacteria.