In collaboration with Monti,1 I found that 95 per cent. of the children of the poor in Vienna showed evidence of a tuberculous infection at the time of puberty. Since then a number of papers on this subject have appeared from various cities and countries. The results were very different. The cause of this variation lies partly in the actual differences in the various cities, but to a certain extent the difference in the method used for the examination and the difference in the selection of the material share the responsibility.
I regard it necessary that the important question of the spread of tuberculosis in definite cities, countries and strata of society should be answered definitely. To this end it is absolutely necessary to use the best methods of examination and to select the material properly.
SELECTION OF MATERIAL
A true picture of the actual conditions can only be