It was not until the beginning of the nineteenth century that Laënnec (1811) described the tuberculous lesion from the anatomical and pathological standpoint. Gürlt pointed out for the first time in 1831 the similarity, the identity in fact, of tuberculous lesions in man and the ox.
In 1865 Villemin showed that tuberculosis could be conveyed from animal to animal, always producing similar lesions, and in 1868 Chauveau proved that, in the calf, infection might arise simply from the eating of tuberculous material.
At a somewhat later date doubts were entertained regarding the identity of human and bovine tuberculosis. Virchow denied the identity of the two diseases on the basis of a comparative study of the lesions. His opinion, however, has not prevailed, and the doctrine of the identity of tuberculosis in mammals still appears probable, in spite of the recent declarations of Koch (1901).
Causation. Tuberculosis is due solely to the activity of the tubercle bacillus. In 1884 Koch isolated and cultivated this bacillus in living animals, and always reproduced typical tuberculous lesions by injecting cultures. In 1887 Nocard and Roux described a rapid method of cultivating the bacillus, and in 1890 Koch announced the discovery of tuberculin.
The tubercle bacillus assumes the form of a little rod, five or six micromillimètres in length, and ·03 to ·05µ in thickness. It has a special staining reaction when treated with Ehrlich’s or Ziehl’s solution. It grows between 98° and 104° Fahr. (37° and 40° C.) in various artificial media containing glycerine.
Healthy subjects become infected by the accidental entrance of germs into their bodies, either by the respiratory and digestive tracts, or through solutions of continuity in the skin.
The material from tuberculous centres is virulent, whether consisting of sputum or discharge, saliva, fæces, urine, milk, etc., or tuberculous tissues derived from the different viscera.
The blood and muscular tissues are not always virulent, even in cases of generalised tuberculosis.
The virulent organisms usually enter the body through the lymphatic system; invasion proceeds from the point inoculated towards the nearest lymphatic glands and thence along the chain of lymphatic vessels, and the lesions extend, attacking the internal organs more or less rapidly. The body does not necessarily become fatally infected as a consequence of accidental or even experimental infection, for the bacillus may itself be destroyed by the phagocytes, or the lesion may remain purely local.
Although tuberculosis is the gravest and most widespread disease on the surface of the globe, its contagious character is relatively little marked, a fact which has unfortunately led to its receiving little attention in ordinary life.