{121} The importance of recognizing the etiology of these tumors rather than their anatomy as a basis of classification was strongly urged by Klebs,[88] who proposed the term infective tumors for the group of granulomata, including syphilis, lupus, leprosy, and glanders; and for tubercle, scrofula and the pearly distemper of animals, which Virchow had classified as lymphomata. This group has been still further extended by the addition of the lymphomata occurring in typhoid fever, scarlet fever, and diphtheria. Ponfick[89] has recently added the disease actinomycosis to the series, and Cohnheim suggests that certain of the lympho-sarcomata may be similarly classified. [Footnote 88: _Prager Vierteljahrschrift_, 1875, cxxvi. 116.] [Footnote 89: _Die Actinomykose des Menschen_, 1882.] The growths thus included have a common element of structure--the granulation-tissue, with its possible disappearance through absorption or its transformation into an abscess or dense fibrous tissue. Such features are those common to the granulation-tissue resulting from ordinary inflammation. Their essential characteristic, however, lies in the etiology of this granulation-tissue, and for many members of the group the cause has been discovered to be microscopic organisms. The constant presence of these is determined in sufficient numbers, in such distribution, and in such relation, as to explain the nature and occurrence of the tumors. The evidence recorded is not equally full and exact for all members of this group. Neisser[90] has discovered the bacillus of leprosy, and the discovery by Koch[91] of the bacillus of tuberculosis, scrofula, and pearly distemper has already been referred to. Schütz and Löffler[92] have lately announced their isolation of the micro-organism causing glanders, and Bollinger[93] discovered the fungus whose presence is necessary for the existence of actinomycosis. [Footnote 90: _Virchow's Archiv_, 1881, lxxxiv. 514.] [Footnote 91: See page 99.] [Footnote 92: _Deutsche medicinische Wochenschrift_, 1882, lii. 707.] [Footnote 93: _Centralblatt für die med. Wissenschaften_, 1877, xxvii.] In the above affections the organisms are to be regarded as the characteristic active agent in producing the phenomena of the disease in which they occur. The presence of micro-organisms in syphilis, typhoid fever, scarlet fever, and diphtheria is admitted, yet their absolute identification and constant presence as a cause of the various manifestations of the respective diseases still remains to be proved.