Stud. Hist. Phil. Biol. & Biomed. Sci., Vol. 31, No. 2, pp. 233–270, 2000 Pergamon  2000 Elsevier Science Ltd. All rights reserved Printed in Great Britain 1369-8486/00 $ - see front matter www.elsevier.com/locate/shpsc Of Lymphocytes and Pixels: The Techno- Visual Production of Cell Populations Alberto Cambrosio,* Peter Keating² Room set at infrared, Mind at ultraviolet, Organisms ever stranger, Hallucinated on the slide, fluoresce:... (James Merrill, Vol. XLIV, No. 3) 1. By Way of a Preface This article grew out of the authors’ participation in a 1992 meeting on ‘Clinical Flow Cytometry’, held in Baltimore by the New York Academy of Sciences. 1 Back then, ‘flow cytometry’ meant to us a sophisticated piece of equipment used mainly in immunology laboratories to perform high-speed counting and sorting of cells out of mixed populations. Our interest in flow cytometry had spun out of previous work on monoclonal antibodies, exquisitely specific reagents that transformed the flow cytometer from an idiosyncratic into a standard (though, initially, still expensive) piece of laboratory equipment; in turn, flow cytometry contributed to the transformation of monoclonal antibodies into a ‘revolutionary’ tool (Keating and Cambrosio, 1994; Cambrosio and Keating, 1995). We knew about the strategic role played by flow cytometry in research, in the constitution of entities known as lymphocyte subpopulations that form the basis of our present understanding of the immune system (Cambrosio and Keating, 1992; Keating and Cambrosio, 1994). Last, we also knew that flow cytometry had surfaced, ‘slowly and painfully’ (Ault, * Department of Social Studies of Medicine, McGill University, 35 Drummond Street, Montreal (QC), Canada H3G 1Y6. ² Department of History, Universite´ du Que ´bec a ` Montre ´al, Montreal (QC), Canada H3C 3P8. Received 13 January 1999; in revised form 10 May 1999. 1 As with any ‘origin’ story, this one is largely a convenient rhetorical device. The meeting in question was: ‘Clinical Flow Cytometry’ (Baltimore, 25–28 April 1992); the proceedings have been published as Landay et al. (1993). PII: S1369-8486(99)00037-0 233