Air,

The general bacterial contamination of the air is identified. The quantity and the positioning of the points for taking samples are established depending on the size of the areas, the number and amount of activity of the people located in it taking into account the possible convectional air flows. On the average it is possible to recommend one point for taking samples for each 20 sq m of area. It is necessary to take the air samples at the respiration level of a sitting or standing person. In investigating employing sampling methods two dishes with conventional nutrient agar are placed at each sampling point to account for the general bacterial inoculation and two dishes with chocolate agar for detecting streptococcus viridans. The period of exposure can be increased to one hour. In highly infected or dusty quarters it is necessary to shorten the period to 10 minutes. The dishes with conventional agar are held for a day in a thermostatically controlled chamber and additionally for a day at room temperature. Then the total number of colonies, which grew on the two dishes, is computed. The dishes with chocolate agar are held in the thermostatically controlled chamber for two days, after which any suspicious colonies are computed.