. Preventive medicine and hygiene. n ahayloft were smitten. It is estimated that a person living in London breathes about 300,-000 microbes in the inspired air each day. The expired air, during normal respiTations, is practically bacteria-free, no matter how many may be contained in the inspired air. Themoist mucous membranes of the upper respiratory passages act as abacterial trap. When the expired air contains bacteria it is only as aresult of coughing, sneezing, talking, or other forced expiratory efforts(see Droplet Infection). The harmful bacteria in the air and the danger of contracting
. Preventive medicine and hygiene. n ahayloft were smitten. It is estimated that a person living in London breathes about 300,-000 microbes in the inspired air each day. The expired air, during normal respiTations, is practically bacteria-free, no matter how many may be contained in the inspired air. Themoist mucous membranes of the upper respiratory passages act as abacterial trap. When the expired air contains bacteria it is only as aresult of coughing, sneezing, talking, or other forced expiratory efforts(see Droplet Infection). The harmful bacteria in the air and the danger of contracting dis-ease through air-borne infection are considered below. Method for Determining Bacteria in the Air.—A rough idea of thebacterial population of the air may be obtained by exposing suitableculture media in Petri plates for various periods of time, and countingthe colonies which develop from the germs falling upon them. A large number of different devices have been described for a more 718 BACTERIA AXD POISONOUS GASES IX THE AIR. Fig. 90.—Magnus As-pirator. accurate determination of the number of bacteria in the air. Theseare all adaptations of three general ;^: (1) filtration of air; (2)bubbling air through some liquid medium; (3) i^reeipitating the bac-teria from a given volume of air. Each of these methods can be madeto give fairly satisfactory results in the hands ofcompetent workers, but the Committee of theAmerican Public Health Association recom-mend the following method of Petri on accountof its simplicity and general applicability: Filtration Method of Petri.—The filtertubes are glass tubes li/^ cm. in diameter and10 cm. long. In the end of each is placed a per-forated cork stopper, through which a glass tube6 mm. in diameter is passed. The filtering ma-terial consists of sand which has been passedthrough a 100-mesh The sand in the filtertube is 1 cm. deep and supported by a layer ofbolting cloth covering the cork. Two filter tubesare connected
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Keywords: ., bookauthorwh, bookcentury1900, bookdecade1910, booksubjecthygiene
