SUMMARYCultures of form 2 mycobacteria, which had been recently isolated from form 1 of strains of Mycobacterium tuberculosis and atypical mycobacteria, were cultivated on nutrient agar in screw-capped bottles and kept unopened for 6 weeks at room temperature. Gram-positive granules developed in organisms which had penetrated into the medium. When these organisms were incubated in digest broth at 37' with intermittent aeration, the granules were liberated into the medium and gradually increased in size to that of a small coccus. After a resting period of about 2 weeks, the ' cocci ' started to multiply independently, forming diplococci and tetrads.At this stage the cocci yielded colonies on subculture on nutrient agar. The cocci were identified as members of the genus Mycococcus, family Mycobacteriaceae, order Mycobacteriales (Krassilnikov, 1959). Mycococci were not obtained in broth cultures which were either not aerated or were aerated frequently or continuously. Prolonged subcultivation of the parent form 2 strains on nutrient agar prevented the development of mycococci in broth. Evidence, such as the failure to isolate mycococci from uninoculated but aerated media, is submitted that the mycococci were not contaminants. Previous work on isolation of similar cocci from different members of the order Actinomycetales, including human and bovine strains of M . tuberculosis is reviewed.

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SUMMARYI n studying 8 strains of Mycobacterium tuberculosis and 7 strains of atypical mycobacteria all 15 were found to produce, in addition to the typical acid-fast cells, non acid-fast ones, which gradually developed intracellular spore-like bodies ; later free-lying spores were seen in the same cultures. This process occurred in heavily inoculated Lowenstein-Jensen medium cultures, which were at least 8 weeks old and were frequently aerated during incubation. With the atypical mycobacteria it occurred more readily in cultures in Kirschner fluid medium than on solid media. When the cultures containing spores were inoculated on nutrient agar plates, endospore-forming, rapidly growing organisms were obtained, which were not acidfast. These organisms when obtained from independent cultures of the same strain appeared to be identical in bacillary and colonial morphology at their first isolation on nutrient agar, but the organisms from different strains showed variation in these characters. Thus mycobacteria appear able to grow in two different forms: ( a ) form 1, which is acid-fast and multiplies by fission only; (b) form 2, which is not acid-fast, produces endospores regularly and can be maintained in pure culture on nutrient agar. A series of phases of development of form 2 cells in the cultures of form 1 organisms in serial smear examination of Lowenstein-Jensen medium cultures is described. It is suggested that mycobacteria might be considered as dimorphic organisms in the same sense as some of the human pathogenic fungi are known to be dimorphic. Evidence is submitted that form 2 organisms are not contaminants.

To the Nuffield Foundation we are particularly indebted; they, by financial ,ssistancc, not only ensured the development of the apparatus but also ils clinical success by their support to the project as a whole.

A case of a 17-year-old patient with exacerbation of a central giant cell granuloma of the mandible during pregnancy is reported. The possible relationship of the giant cell lesion to a pre-existing fibrous dysplasia is considered although there was lack of histological evidence.A 17-year-old healthy female patient was referred by her dentist for evaluation of a lesion in the area of a missing mandibular left third molar. The only relevant dental history was the removal of the third molars 3 years earlier. The panoramic film taken at that time revealed cyst-like radiolucencies around the apical region of the second molar and continuous with a mixed radiolucent-radiopaque lesion that extended to occupy the anterior half of the ascending ramus. There was slight expansion and the internal aspect had a granular bone pattern consistent with a fibro-osseous lesion. A biopsy resulted in a histopathological diagnosis of an aneurysmal bone cyst. One month later the lesion in the body of the mandible was completely curetted. The patient returned 8 months later complaining of a hard bone-like swelling on the buccal aspect of the alveolar process adjacent to the left mandibular second molar. A panoramic radiograph revealed non-uniform repair of the previous surgical procedure (Figure 1). The patient was monitored with another panoramic film in 6 months (Figure 2). At that time the films were submitted for a radiological opinion. Of note was the finding that although there were changes in the body of the mandible secondary to the surgery, the granular bone pattern of the portion of the lesion in the ramus had not changed. The radiological opinion was that the appearance was most consistent with fibrous dysplasia.After another 6 months the patient returned complaining of pain and a considerable swelling of rapid onset. At that time she was in the fourth month of her pregnancy. A panoramic film taken at that time