Tubercle

1. A small knoblike prominence or excrescence, whether natural or morbid; as, a tubercle on a plant; a tubercle on a bone; the tubercles appearing on the body in leprosy.
2. (Med.) A small mass or aggregation of morbid matter; especially, the deposit which accompanies scrofula or phthisis. This is composed of a hard, grayish, or yellowish, translucent or opaque matter, which gradually softens, and excites suppuration in its vicinity. It is most frequently found in the lungs, causing consumption.
Tubercle bacillus (Med.),
a minute vegetable organism (Mycobacterium tuberculosis, formerly Bacillus tuberculosis, and also called Koch's bacillus) discovered by Koch, a German physician, in the sputum of consumptive patients and in tuberculous tissue. It is the causative agent of tuberculosis.