The authors believe that the widespread use of isoniazid and streptomycin is responsible for a change in the pathology of pulmonary tuberculosis. This belief is based mainly upon the histological examination of 69 surgical specimens from patients who had been treated with either one or both of these substances, given usually in combination with PAS. They noted differences in the pathology of the lesions depending on whether the patient had been treated with streptomycin or isoniazid, and these differences are attributed to the differences in the actions of the drugs-streptomycin is essentially tuberculostatic and penetrates very poorly into cells and caseous material, whereas isoniazid is tuberculocidal and penetrates very readily.

The essential changes in the pathology ascribed to streptomycin therapy were: (1) in miliary tuberculosis the lesions were sharply outlined and fibrosed, but when caseation remained there was exaggeration of the surrounding collagen and tubercle bacilli were still present; (2) there was a marked diminution of perifocal reaction around large tuberculous processes and the alveoli were empty; (3) bronchiolar disease was quantitatively reduced, scarring was rare and there was healing with re-epithelization at the bron-chocavitary junction. With isoniazid therapy the essential changes were: (1) atypical giant cells, containing 6-50 nuclei, and often distantly situated from the acute processes; (2) an increase in randomly situated xanthoma cells and the presence of calcified Schaumann bodies; (3) granulomatous reactions resembling those of Boeck's sarcoid, often containing non-caseous central necrosis; (4) atypical proliferation of smooth muscle around bronchioles was not uncommon, and there was an abundant collagen formation; (5) the presence of smooth, glistening and trabeculated linings to some 19% of cavities, whose walls were fibrous, markedly thinned, haemorrhagic and hyperaemic, and when communicating with the outside, the proliferating bronchial epithelium was often extended along the inner surface. S. R. M. Sushby.