Abstract
We shall describe the dissociation of a tubercle bacillus of low virulence, originally of bovine origin, which was isolated by Calmette in 1908, and passed through 230 subcultures on a special bile medium. It is claimed that at the time of isolation it produced lesions in rabbits, but after long cultivation it has lost its pathogenicity for small laboratory animals. The organism is designated as “B.C.G.” (Bacillus Calmette-Guérin) and for the last five years has been extensively used for vaccinating children, with the object of attaining prophylactic immunization.
The cultures in our possession were obtained from three different sources. The first was received from Dr. Watson of Ottawa, Canada, and the second was brought from Paris by Dr. Lawrason Brown in the spring of 1926. After seeding this second culture on Sauton's fluid medium, growth and cultural differences were noticed in some of the flasks, and it was dissociated into two distinct types of colonies.
However, the study reported here on dissociation was carried out with the third culture, which came direct from the Pasteur Institute, sent to us by Professor Calmette. As soon as it was received it was suspended in salt solution and filtered as described previously, 1 and inoculated on the surface of gentian-violet medium plates. After a period of 5 to 6 weeks' incubation, two distinct types of colonies were seen. One of the colonies predominated in large numbers. From one of the plates two colonies, having different characteristics, were removed and again cultivated. This procedure was repeated until dissociation was well established. It can be seen from the photographs that these two colonies have distinct cultural characteristics. Colony R is very waxy, the folds are very smooth and raised, extending from the center to the periphery. The periphery is clean cut, rounded, slightly raised and does not extend into the medium.
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