[Circadian rhythm of air-borne bacteria and dust particles in a mouse breeding room]

The circadian rhythm of air-borne bacteria and dust particles in a mice breeding room was studied at 1-hour intervals on the first, third and fifth day after accommodation of the animals. The numbers of air-borne bacteria in the room increased day by day after accommodation, and showed a circadian rhythm which went down at about noon and rose with three peaks at about 20:00, 1:00 and 8:00. The numbers of dust particles tended to decrease from day to day, and they showed almost the same circadian rhythm as the air-borne bacteria. Correlations between air-borne bacteria and dust particles were not significant for each particle level on the first day, but were significant for all the particle levels of 0.3, 1, 2, and 5 microns at the third day, and were also significant at particles levels of 0.5 micron or more on the fifth day.