2. =Surgical Operation.= A very large part of the material obtained for pathologic examination is removed by the surgeon for diagnostic purposes. The question of the surgical technique employed may be left to the surgeon, but as far as the pathologic aim is concerned certain principles should be followed, if the object of the examination is to be secured. Unfortunately these principles are not recognized by the great majority of practitioners, and pieces of tissue to be examined are taken at haphazard from the surface or from necrotic areas, to be run through by the pathologist, only to find that no diagnosis is possible, either because the portion of tissue removed did not extend deeply enough or is wholly necrotic. Great care and judgment should be exercised in the choice of the portions to be removed for diagnosis. The part removed must be characteristic of the condition present. It is necessary not only to ascertain the character of the pathologic change but also the nature of the reaction in the surrounding tissue. A neoplasm may show the histologic structure of an adenoma, but at its periphery may be found infiltrating the neighboring tissues as an adenocarcinoma. If the piece of tissue for examination is removed from the central part or surface of the tumor, an incorrect diagnosis may be given. This is especially true in the case of rectal and uterine polypi, papillomata of the mouth and penis, horny warts, etc. The rule to be followed in all cases is that the excised portion must be at the boundary-line of the neoplasm or morbid process, and extending across it so as to include both pathologic and surrounding normal tissues. The cut must be deep enough to extend into living tissue, and in the case of epithelial surfaces to go below the basement membrane. It should be made at right angles to the surface. Necrotic, softened, or degenerating portions should be avoided, unless a portion of this is removed in addition for the purpose of ascertaining the nature of the degenerative changes present. The scraping away of superficial scabs, exudates, etc., should never be practiced for purposes of diagnosis. Time is saved if a satisfactory excision be made the first time, and to secure this the tissue must be living, the cut must be deep enough, and the portion removed must fully represent the nature of the condition present. When organs are removed, as in the case of the appendix, uterus, tubes, ovaries, mamma, etc., several portions of tissue representing different structures of the organ should be secured for the examination.