| Popis: |
1.1. An apparatus is described which is adapted to direct determination of the number of pollen grains or other particles in known volumes of air, with which abrupt changes in counts can be easily followed. 2.2. It is confirmed that the Scheppegrell-Cocke formula for calculating air pollen concentration from the results of gravity slide experiments is approximately correct. The main sources of error are the effect of wind on the counts and the determination of the effective diameter of the particles. 3.3. No consistent diurnal changes in pollen counts could be detected under the conditions of the experiments. 4.4. Rain quickly and completely freed the air from pollen, but other short-time effects of weather were negligible except for a shower of palm pollen during a sudden shift of wind, which was attributed to a nearby group of trees. 5.5. A series of runs made indoors showed vividly the effect of ordinary house cleaning methods on the dust content of the air, and especially on its pollen content. The possible significance of pollen from cut flowers is discussed in this connection. 6.6. A review of the problems involved in air pollen assay shows that the gravity method has several unique advantages over other methods which are practicable at present, while it has no serious disadvantage if pains are taken to avoid the common faults in the design and arrangement of the exposure station. 7.7. It is suggested that pollen counts be reported as index figures, that is, as percentages of specified, arbitrarily adopted, standard counts for each type of pollen, in order to avoid the erroneous implications inherent in previously employed counting scales. |
