Immunoglobulin (IgG, IgA, IgM) values in a few population groups.

Certain significant differences were found between the mean IgG levels in four different population groups. No differences were found in the IgA and IgM classes. The highest IgG levels were found in food workers and the lowest levels in coal-miners working at the face. Surface mine employees and employees just taken on for underground work had intermediate values. On dividing the population groups into age sub-groups, significant differences were found between some of the latter. Physical stress, differences in exposure to infections, the influence of the macro- and micro-climate and spontaneous and controlled selection for given occupations are regarded as possible causes of the observed differences.