The intimacy of relation between tuberculosis and pearly distemper is a necessary result of Villemin's[62] experiment, in which the rabbit became tuberculous after inoculation with fragments of the pearly tumor. Gerlach,[63] and especially Schüppel,[64] showed that the structure of the nodules of the pearly distemper is the same as that of the tubercles of man, and that the two diseases are identical from the histological point of view. [Footnote 62: _Op. cit._, 537.] [Footnote 63: _Virchow's Archiv_, 1870, li. 290.] [Footnote 64: _Ibid._, 1872, lvi. 38.] From the anatomical identification and the etiological connection, as shown by Villemin, Gerlach, and Aufrecht, the pearly distemper became designated as a bovine tuberculosis. The experiments of Villemin were further productive in leading to the discovery by Koch of the bacillus tuberculosis. It was early obvious that certain cheesy material and gray tubercles possessed the infectious qualities, and Villemin[65] maintained that the immediate cause of the latter was a germ introduced from without, which propagated and perpetuated itself in man and certain animals. This view acquired prominence through the investigations of Klebs, who in 1877 claimed to have isolated the micrococci which produced tubercles when injected into animals. Three years later Schüller[66] confirmed the statements of Klebs, and asserted that he had been enabled to obtain infective micrococci by cultivation from {100} miliary tubercles, scrofulous glands and joints, and from the tissue of lupus. Aufrecht[67] found micrococci, single and in chains, and short glistening rods, within tubercles resulting from inoculation with material from pearly tumors. The same organisms were found in tubercles produced by the inoculation of tubercles from man, and he regarded these rod-shaped bodies as the specific element productive of miliary tuberculosis. [Footnote 65: _Op. cit._, 620.] [Footnote 66: _Op. cit._, 55.] [Footnote 67: _Pathologische Mittheilungen_, 1881, p. 43.] The isolation of the virus of tubercle was thus regarded as an open question till the announcement by Koch[68] of the constant presence of a hitherto unknown, characteristic, well defined organism in all tuberculous affections, which, when isolated and introduced into animals, produced tuberculosis, the resulting tubercles likewise containing the organism. [Footnote 68: _Berliner klinische Wochenschrift_, 1882, p. 15.]