{101} The discoveries of Koch thus show that the production of tuberculosis is dependent upon the presence of distinctive bacilli, and that these bacilli are present not only in miliary tubercles, but in scrofulous glands and joints, in cheesy inflammation of the lungs, and in the pearly distemper of animals. The identification of tuberculosis with the pearly distemper and certain scrofulous affections is thus established from the etiological as well as the histological point of view. As the bacilli are to be regarded as the virus of tuberculosis, so their introduction into the human body is necessary for the production of this disease in man. It is obvious, however, that other factors than the virus are necessary, for not every one exposed to the reception of tubercular bacilli becomes tuberculous. It may well be that scrofula is still to be regarded as that condition of the solids and liquids of the body which offers favorable opportunities for the retention and growth of the bacilli, and thus for the production of tuberculosis. Formad[70] claims that he has discovered structural peculiarities of tissue as a cause for the scrofulous habit, which he regards as synonymous with a predisposition to tuberculosis. These peculiarities are manifested by a narrowness of the lymph-spaces and their partial obliteration by cellular elements. He also maintains that these features are not only of congenital origin, but may be acquired through malnutrition and confinement. [Footnote 70: _Studies from the Pathological Lab. of the Univ. of Penna._, reprint, 1882, xi. 3.] The occurrence of a local, circumscribed tuberculosis in extreme old age, without antecedent or other concurrent evidence of scrofulous disturbances, suggests that favorable opportunities for the development of the tubercular bacillus may arise in advancing years. In like manner, the frequent termination in phthisis of cases of diabetes suggests the likelihood of tuberculous inflammation arising in the absence of any evidence of previous scrofulous or tuberculous disease. The scrofulous condition or constitution, as indicated by vulnerable tissues, with a protracted course of inflammations, and a persistence of their products, with a tendency to cheesy degeneration, may still exist without a sign of tuberculosis. Those who claim that scrofula and tuberculosis are identical must, in the light of Koch's discovery, demonstrate the presence of the bacillus in all scrofulous inflammations, and deny the existence of scrofula apart from indisputable manifestations of the activity of the bacilli of tuberculosis. It may be that such evidence will be presented; until it is collected scrofula and tuberculosis are to be regarded as distinct though often coexistent. The scrofulous person is frequently tuberculous, the tuberculous person is usually scrofulous; the non-scrofulous person, however, may die of tuberculosis, while the individual may be scrofulous without containing tubercle.