An ancient concept that took modern form around 1900, focal infection theory was widely accepted in medicine by the 1920s. In the theory, the "focus of infection" might lead to secondary infections at sites particularly susceptible to such microbial species or toxin. Commonly alleged foci were diverse—appendix, urinary bladder, gall bladder, kidney, liver, prostate, and nasal sinuses—but most commonly were oral. Besides dental decay and infected tonsils, both dental restorations and especially endodontically treated teeth were blamed as foci. The putative "oral sepsis" was countered by tonsillectomies and tooth extractions, including of endodontically treated teeth and even of apparently healthy teeth, newly popular approaches—sometimes leaving individuals toothless—to treat or prevent diverse diseases.