In the late 1940s, a microanatomist from London Ontario, Murray Barr, discovered 
a mark of sex chromosome status in bodily tissues, what came to be known as the 
'Barr body'. This discovery offered an important diagnostic technology to the 
burgeoning clinical science community engaged with the medical interpretation 
and management of sexual anomalies. It seemed to offer a way to identify the 
true, underlying sex in those whose bodies or lives were sexually anomalous 
(intersexuals, homosexuals and transsexuals). The hypothesis that allowed the 
Barr body to stand in for 'chromosomal' or 'genetic' sex was provisional, but it 
supported the expectation that genetic information established one's primary 
identity, and the conviction that the animal world could be neatly divided into 
two, and only two, sexes. Ultimately, this provisional hypothesis, and its 
status as an unambiguous arbiter of true sex, was overturned. But during much of 
the 1950s, Barr's thesis about the identity of the Barr body was consistent with 
a coherent set of theories and evidence explaining sexual development and sexual 
pathology. Though provisional, the scientific status of the sex chromatin within 
this system of knowledge was good enough to support a flourishing research 
enterprise in the clinical sciences.