Rita,
Sirius Red works like Congo Red in that the elongated molecules line up
with collagen so that the long axes are parallel.  Check Histochemistry
(1982) 74:153-156.  Puchtler and Sweat of Congo Red fame also
checked out Sirius Red in ancient times: Archives of Pathology, Vol.78,
July 1964, pp.69-72.
Bob Santoianni
Emory University Hospital
Atlanta, Georgia
robert_santoianni@emory.org