BACTERIAL CONTENT or THE ATMOSPHERE OF THE LONDON UNDERGROUND ELECTRIC RAILWAYS.—Previous work on this subject is almost limited to a report by F. W. Andrewes in 1902 on the air of the Central London Railway and to a study by G. A. Soper in 1904 of the air of New York subways. Dr. J. Graham Forbes carried out an investigation in 1920 of the air of six London electric railways (Journ. of Hygiene, vol. xxii, 1924, p. 123). The average of all results does not compare unfavourably with the outside air of London. The ratio of the number of organisms which develop at room temperature (about 20° C.) is about 14 for railway air to 10 for outside air, but the ratio for organisms developing at body temperature (37° C.) is considerably higher, namely 2 to i respectively. The mean number per litre of air, for room temperature organisms, is about 9 in railway air and 6-3 in outside air; for body temperature organisms, 4-6 in railway air and 2-2 in outside air. Increase or decrease in passenger density in the cars is generally, but not always, associated with a rise or fall in the bacterial content of railway air, affecting both groups of organisms; the actual number of organisms is affected by other factors, such as fluctuating air currents and move ments of passengers. The bacterial content of platform air is generally higher than car air, probably on account of the greater amount of draught and dust disturbance.—The bacterial content of car air was lowest on the Central London and highest on the City and South London, the latter being about 34 per cent, more than the former. The organisms comprised a number of species of micrococci, bacilli, sarcinae, yeasts, streptothrices, and moulds. While some of the organisms met with occur in the mouth, nose, and on the surface of the body, in no instances were pathogenic organisms specifically proved to be present, other than certain moulds, e.g. Aspergillus niger and A. fumigatus.