Microbic dissociation in the acid-fast bacilli with special reference to the biological characters and virulence of the bacillus of calmette and guérin (B.C.G.)
1. Evidence of microbic dissociation as shown by variation in colonial form has been found. The types found were 'rough', 'smooth', and 'intermediate'. The great majority of colonies were of the ' intermediate' -type. The 'rough' type of colony corresponded closely with that described by Petroff, but the 'smooth' type did not.2. Evidence of microbic dissociation' was also found with two other acid -fast bacilli, namely the smegma bacillus, and one of Clegg's leprosy bacilli, 'rough' and 'smooth' colonies being found.3. Experiments on guinea -pigs have not shown clean cut lines of demarcation between the 'rough' and 'intermediate' types of colony, but definite variation was found, the 'smooth' type being most virulent, the 'rough' type second in virulence, and the 'intermediate' type the least virulent. Evidence of invasion of internal organs following subcutaneous injection was found in all types.Petroff, though finding the 'R' type relatively avirulent, found evidence of tuberculosis following intra-ventricular inoculation with 'R' type, two animals dying from this cause on the 266th and 375th days, and in one animal lesions were found in the spleen following intra-testicular injection with 'R' type.Be considers that these results may have been due to 'S' type organisms still remaining in the 'R' culture, and as there are considerable difficulties in separating them completely, this may be an explanation in my own experiments.4. On inoculating guinea-pigs with a subculture of B.C.G. on Dorset's egg-medium, results showed that the culture was more virulent than the 'intermediate' type of growth. This would seem to be explained by Petroff's finding that the 'S' type of organism did not grow on glycerol-bile-potato medium, but that it grew on ordinary media.Subcultures of B.C.G., therefore, on ordinary media would tend to grow more and more virulent.5. In the time at my disposal no guinea -pigs died following subcutaneous inoculation of any of the types of organism, although many showed active lesions¡ in internal organs which might have lead to a fatal issue had time permitted. Petroff, on the other hand, did have deaths following subcutaneous inoculation of the 'S' type, but on the 103rd day, a longer period than I allowed in my experiments.Another interesting point is that of forty-two guinea-pigs five died of ill -defined intercurrent diseases and these five were among the 21 which received intra-ventricular inoculations.Death occurred on the 18th day or later, and it is possible that these deaths were due to pathological conditions produced by the inoculations although not, apparently, tuberculosis.6. The types of lesion found were aggregations of lymphocytes and large mononuclear cells, but no giant cells were found. Occasionally necrosis, and in many cases fibrosis, was present
