Dust and its dangers / by Mitchell Prudden.

  • Theophil Mitchell Prudden
Date:
[1890], ©1890
Catalogue details

Licence: Public Domain Mark

Credit: Dust and its dangers / by Mitchell Prudden. Source: Wellcome Collection.

    38/146 (page 18)
    colonies which develop on the surfaces, get at least an approximate idea of the relative num- ber of suspended bacteria slowly settling in the air of the different places (see Fig. 2). We cannot, of course, by this method say how many germs were present in a given vol- ume of air, as we can by the more elaborate and accurate method given above, and there are many minor sources of error. For exam- ple, the mould spores are so very light and buoyant that they fall but slowly, so that we may altogether miss many of them, and the same may be true of some of the lighter bac- teria. Moreover, even very slight upward air currents may interfere with the settling of the germs, and in windy places this method is of little use. But on the whole, if similar condi- tions are maintained in the different analyses, comparative results may be obtained in this way which are of much value, as we shall pres- ently see. This, which we will call the plate-method, enables us to get a general notion of the bac- terial contents of the air in various places under conditions which would render the use of the