The evidence as to the percentage of the total population showing evidence of old tuberculous lesions is derived from hospital practice. Tuberculosis is due to a specific bacillus. Tuberculosis has been produced experimentally in animals by the introduction of this bacillus, in inspired air or with food. Man is subject, example in infected households and workshops, to the conditions which have been proved experimentally to produce tuberculosis in animals. General Considerations on the Statistical Study of Histories of Infection in Phthisis. The cases illustrate the types of history often obtained in investigating cases of phthisis. For many years, the authors have carefully investigated the history of all cases of phthisis notified in Brighton. From 1902 onwards a large proportion and during the last year over half of these patients have been treated in the Borough Sanatorium.