Many of Manhattan's leading physicians drew a link between tuberculosis and congestion in the City's tenement houses. Physicians attributed 8,000 to 9,000 deaths a year to tuberculosis, mostly in the poorest and most unsanitary neighborhoods of the City. Yet conditions in tenement houses may have been influenced not only by crowding, but also by the construction and use of the tenement itself. Hermann Biggs, the New York City Health Commissioner who waged a campaign against tuberculosis in the late nineteenth century, argued that while population density generally could be considered a good indicator of mortality, this did not always hold true for New York City. Biggs found that "in some of the wards where the density of the population is the greatest the mortality has been below the average, and in other wards with a relatively scarce population the mortality has been extremely high."
All tenement houses constructed after the passage of the 1901 law were referred to as "new law" tenements. In 1900 the New York State Legislature created the New York State Tenement House Commission, which created a separate Tenement House Department for the City of New York. The Tenement House Department was instrument in pushing through the Act of 1901. This most recent tenement house legislation reinforced the need for ventilation and light in ameliorating the morbidity and mortality that characterized life in the tenement house districts.