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A model system of exfoliated normal human cervicovaginal squamous cells, exfoliated rodent tumor cells, and acellular, viscous, mucuslike material was used to investigate cell deposition on smear preparations made with three different instruments: plastic spatulas, wooden spatulas, and brush-tipped collectors. The total number of exfoliated cells and the total number of tumor cells present within the randomly distributed holes were then recorded for 41 smear preparations. For smears done with the brush, a total of 47,146 exfoliated cells were recorded; with wooden spatulas, 4517 cells; and with plastic spatulas, 7648 cells. When the brush was used, 6905 tumor cells were recorded. When wooden or plastic spatulas were applied, 563 and 1132 tumor cells were found, respectively. Thus, the brush yielded 12.2 and 6.1 times more tumor cells than plastic and wooden spatulas, respectively.

A model system consisting of exfoliated abnormal cells and acellular viscous, mucus-like material was used to investigate the effect of the pressure exerted during smearing on the number of abnormal cells present in the preparations. Smears were made with a cotton swab applicator from left to right with parallel strokes, without overlapping smearing and without rotating the instrument of cell collection. Light and heavy pressures done during smearing procedure were recorded by the aid of an automatic scale. By means of the smearing technique, a gradual decrease in the total number of cells was recorded along the pathway of smearing. By using heavy pressure, however, cell accumulation also occurred at the end of the pathway of the last smearing strokes. Smears made with heavy pressure contained 13% more tumor cells than those made with light pressure. It is concluded that the pressure exerted by the operator during smearing may be an important parameter influencing both the number and the distribution of abnormal cells on smear preparations. These considerations may be of significance in screening programs for tumor cell detection.

A model system of 85% exfoliated normal human cervicovaginal squamous cells, 15% exfoliated rodent t-mor cells and acellular, viscous, mucus-like material was used to investigate the distribution of cells on smear preparations. Smears were made by the same individual with wooden spatulas, using traditional smearing motions. The presence or absence of normal squamous cervicovaginal cells and of tumor cells in ten randomly distributed areas was recorded. Smears made with counterclockwise circular motions contained the largest number of tumor cells, and those with zigzag strokes contained the least. Independent of the motion employed, the largest number of tumor cells was found in ring 9 and the lowest in rings 4 and 10. Some of the factors influencing the accumulation of tumor cells in certain areas of the slide may be: unequal pressure of the spatula during smearing, variations in the angle between the instrument and the surface of the slide and the displacement of tumor cells to certain areas of the preparation by overlapping smearing.

A model system of exfoliated normal human cervicovaginal squamous cells, exfoliated rodent tumor cells, and acellular, viscous, mucus-like material was used to investigate the gradient of cell deposition on smear preparations. Smears were made from left to right with parallel strokes, without overlapping smearing and without rotating the instrument of cell collection. With this technique a gradual decrease in the total number of cells was recorded along the pathway of the smear. The proportion of tumor cells, however, increased halfway along the smearing pathway. The midway increase was significant for wooden spatulas or cotton swab applicators but less marked for plastic spatulas. It would appear that normal squamous cervicovaginal cells, because of their large flat surface, attach readily to the flat surface of the slide and become "consumed" from the material carried by the instrument. On the other hand, the relatively smaller round tumor cells are "pushed" forward by the instrument during the smearing procedure. These considerations may be of significance in screening programs for tumor cell detection.

A model system of 15% exfoliated tumor (Ehrlich ascites) cells and 85% exfoliated cervicovaginal human squamous cells and acellular viscous mucuslike material was used to investigate the distribution of tumor cells on smear preparations. The smears were taken by the same individual, with plastic spatulas, using traditional smearing motions. The presence or absence of normal squamous cervicovaginal cells and tumor cells was recorded in 400 randomly distributed areas. Smears done with circular motions contained the largest number of tumor cells and those done with back-and-forth strokes, the least. Circular motions apparently should be preferred if the purpose is to transfer to slides the largest possible number of tumor cells. Independently of the motion employed, the largest total number of tumor cells was found in ring 9 and the lowest, in ring 5. When the various motions were taken into account, the largest number of tumor cells was found in ring 9 for smears done with zigzag strokes; the lowest, in ring 5 with clockwise circular motions. Despite these differences, comparative studies indicate that plastic spatuls may induce a more even distribution of tumor cells onto slides than wooden spatulas or cotton swab applicators. We have been unable to confirm that plastic spatuals induce better cytologic preparations than do wooden spatulas or cotton swab applicators.