An investigation into the probable influence of environmental factors on the incidence of extrapulmonary tuberculous infections and into the possible explanation of their effect on regional differences in the proportional frequency of the type of infecting strain of the tubercle bacillus has been described.

The importance of substandard housing and of family history in infection with the human type of the tubercle bacillus, particularly in children, has been noted.

Circumstantial evidence of both low economic resources and milk supply influencing infection with the bovine type of the tubercle bacillus pointed to these factors being important in childhood.

I wish to acknowledge the co-operation I received from the Medical Officers of Health for the several Local Authorities within the county of Lanark.