Counting human chromosomes before 1960: preconceptions, perceptions and predilections.

In 1956 the biomedical world was surprised to hear a report that human cells each contained forty six chromosomes, rather than the forty eight count that had been documented since the 1920s. Application of available techniques to culture human cells , halt their division at metaphase, and disperse chromosomes in an optical plane permitted perception of visual images not seen before. Researchers continued to obtain the preconceived forty eight counts until reeducation with these novel epistemic 'chromosomes' convinced them that they could confidently report forty six chromosomes per cell. Within only a few years, and virtually without dissent, the social community of human cytogeneticists agreed upon a shared visual culture of human chromosome count and morphology. The initial forty six count proved not to be an anomaly. A new comparison of historical and ethnomethodological studies has suggested a better understanding of how applied technologies coupled with altered human perceptions established a new science. Human cytogenetics then collaborated with medical genetics to correlate changes in the new human karyotype with disorders of clinical significance.