In Chicago in 1916 an effort was made by the Commissioner of Health to establish relationship between dark rooms and tuberculosis and similar bronchial infections. Careful measurements of light intensities in several thousand rooms, correlated with the frequency of tuberculosis and other illnesses in those same rooms, failed to reveal what it was expected such comparisons would reveal. Health Commissioner Robertson said of this study:

1 Address before the Tenth National Conference on Housing, Philadelphia, June 28-30, 1929, published in Housing Problems in America (National Housing Assoc, 1929), pp. 125-33.

So far as our figures are concerned, we can see no way to connect directly high records in the number of tuberculosis cases with high records in the number of interior rooms. No one likes dark rooms, and there seems to be no defense of them, but with the ideas that prevail about germ diseases, we cannot write them down as the chief cause in the spreading of disease.

In Detroit a few years ago Deputy Health Commissioner W. F. Walker prepared a series of charts showing the frequency of disease in the various sections of the city. These likewise failed to reveal the direct relationship that had been expected. Certain definite correlations were established, but these were not of primary importance.

Mr. Walker did make an important contribution, however. As a result of studying a number of cases where rickets had occurred in tenement building, he ascertained that the average intensity of light within the rooms in which rickets occurred was less than one-half of one per cent of the outside daylight intensity at the same time; whereas examinations of numerous other rooms of the same kind - in which light in excess of that average percentage was found - revealed an absence of rickets. No one can say, however, on the basis of Mr. Walker's examinations, that one-half of one per cent of the outside light intensity within a room is sufficient to prevent the development of rickets; but it is an indication that may have considerable significance.