BCG vaccine bacilli that seemed less virulent, and changed the course of their research to see if repeated subculturing would produce a strain that was attenuated enough to be considered for use as a vaccine. The BCG strain was isolated after subculturing 239 times during 13 years from virulent strain on glycerine potato medium. The research continued throughout World War I until 1919, when the now avirulent bacilli were unable to cause tuberculosis disease in research animals. Calmette and Guerin transferred to the Paris Pasteur Institute in 1919. The BCG vaccine was first used in humans in 1921. Public acceptance was slow,
Abell 1201 BCG s within 5 kpc rising to 360 km s at 20 kpc distance. The BCG also acts as a gravitational lens, bending the light of a more distant background galaxy (at redshift 0.451) into an apparent tangential arc about 6 kpc to one side. This makes the galaxy an important case in investigations of the intrinsic properties of dark matter. Detailed models of the lens mass distribution, starlight and stellar kinematics indicates that the galaxy cluster's dark halo has a shallow inner density gradient and perhaps a soft dark matter core. At face value, this is incompatible with the dark