Suspensions of Pseudomonas aeruginosa, Staphylococcus aureus, Escherichia coli, Klebsiella aerogenes and micrococci were tested for survival on drying and after drying in the atmosphere. The proportion of Gram-negative bacilli that died during drying was greater than that of the Gram-positive cocci, but survival after drying was similar in the two groups of organisms. There were considerable differences in the death-rates on drying of different strains of bacteria, which were consistent on replicate sampling.

A suspension of Ps. aeruginosa prepared from cells which had survived one drying showed a considerably higher proportion of survivors on a second drying; suspensions prepared from subcultures of the dried cells, however, showed a death-rate on drying which was similar to that of the original culture.

Strains of Ps. aeruginosa isolated from floor dust showed a significantly higher proportion of survivors immediately after drying than strains from patients, but the proportion of survivors after 24 hr. of exposure to the atmosphere was approximately the same in the two groups.

Tests were made for survival of Ps. aeruginosa and Staph. aureus in deionized water, tap water, physiological saline and Ringer's solution. In deionized water, Ps. aeruginosa showed a rapid initial loss but some survival for several weeks; Staph. aureus, on the other hand, showed an initial increase in numbers but no survivors after 48 hr. In Ringer's solution all strains of Ps. aeruginosa multiplied rapidly and survived for many weeks; Staph. aureus died rapidly and no strain could be detected after 4 days.

We are grateful to Dr M. T. Parker and Mrs E. Asheshov for the typing of strains of Pseudomonas aeruginosa.