An evaluation of the Coulter model S.

This report is concerned with the performance of the fully automatic counter Coulter model S. The apparatus consists of four units two of which, the electrical power and the vacuum and air pressure units, may be placed under the bench. The counter itself and its printout must be sited side by side on the bench (Fig. 1). Apart from what can be seen on the front, the cabinet conceals a mass of electrical, hydraulic, and pneumatic apparatus some of which is shown in Figure 2. To operate the counter is simple. The sampling tube A (Fig. 3) is placed in the blood container and the bar pushed. As soon as the light behind the bar changes to red, the sample is removed, the form fed into the printout and some 40 seconds later, after some hissing and gurgling, the printer thumps out the form with the results of the haemoglobin, red cell count, white cell count, packed cell volume, mean corpuscular volume, mean corpuscular haemoglobin concentration, and mean corpuscular haemoglobin. The apparatus aspirates 1.2 to 1.3 ml of blood, most of which is used to flush out the previous sample, only 44.7 cmm being used for the measurements. The machine can count a diluted capillary blood sample fed into a second sample tube B (Fig. 3). The dilution required is 44.7 cmm in 10 ml but as it will accept volumes ranging from 9 to 11 ml, 40cmm can be diluted in 9 ml buffered saline and this results in an undercount of only 0.5 %. The counting rate is theoretically 180 per hour as the machine is capable of accepting a new sample every 20 seconds. In practice, feeding in samples and forms takes a little time and the fastest I have achieved, working alone, is 121 counts in 50 minutes, a rate of 145 per hour. The forms used at present are purchased from Coulter Electronics but we are designing a request form which will also be a report form, and as all the results will be on the left hand side, it is suitable for serial reporting (Fig. 4). The size of the form and the initial seven results are dictated by the printout of the apparatus. (An interface is now available which will punch the results on punch tape as an additional or alternative method of recording.)