The agglutination reaction is the easiest to perform and is probably the most widely used of the serological tests for the detection of H. pertussis antibodies. Two methods have been used, a slide test and a tube test. A comparison of these techniques has been made by a number of workers (Evans and Maitland, 1939;Mishulow, 1942; Powell and Jamieson, 1942; Powell, 1944;and DeGara and Mayer, 1947 The Laboratory of Hygiene is currently conducting studies on the immunization of children against diphtheria, tetanus, and whooping-cough. The volume of the individual serums is frequently limited, so that tests requiring small amounts of sera are of definite advantage. For this reason the practicability of a slide test for the determination of H. pertussis agglutinins was considered. The uncovered slide technique was found unsuitable for quantitative work because the test materials dried rapidly and end-results were difficult to interpret. It was therefore decided to investigate the usefulness of concavity slides, covering the depressions with glass cover slips to prevent evaporation. The results of these tests are described in this paper. Procedure Materials.-The following were used: Concavity Slides.-Slides* measuring 2 x 3 in., with 10 polished concavities, 15 mm. in diameter and 1.5 mm. deep, were used.Cover Slips.-Circular microscope cover-slips were used, having the same diameter or a slightly smaller one than that of the depressions. Cover slips with larger diameters were found unsuitable as they were easily displaced during the rotation, resulting in the loss of test materials.Rotating Machine.-Because of its convenience, a Fisher-Kline rotator timed to run for four minutes at 280 revolutions per minute was used. Other rotators giving a similar rotary motion in a horizontal plane might prove equally satisfactory.Pipettes.-Pasteur pipettes with tips carefully prepared so as to deliver drops of constant size were used. The number of drops per test varied, depending on the diameter of the tip.

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